So I just started this game yesterday, and I was wondering, what happens once that 3 day shield is gone?
1) Your wall gets damaged/destroyed
2) You lose any resources your vault cannot protect
3) If you're not sheltered, your troops get injured and sent to the infarmary when you can recover them with resources. If your infarmaries become full, any excess troops permanently die.*
4) If all your troops are defeated, you lose your leader temporarily. You lose any talent point and equipment benefits without your leader.*
*Situational: Depends on whether or not your leader/troops where sheltered or not, so in summary, just remain sheltered and you'll be fine.
I would also like to mention not to stress over losing your wall, it's not something you should bother yourself with as it's useless for the most part.
Small things to note on the post above:
1< Your wall doesn't get "destroyed", as in, it won't lose any levels. Your wall's HP will drop to 0, and it will be 'on fire' for 30 minutes after the attack. After that, it'll slowly repair. Your wall won't ever lose any levels.
4< You only lose your leader when your castle is level 10 or above. Then, it will be put in that assaulter's prison for a few hours. If your castle is above level 17, it will stay there for several days, in which time that player can execute your leader (They will also need a level 10 / 17 respectively castle for this to happen.)
Contrary to what Maintained says, I would actually not neglect your wall either. The "wall is useless" meta-thought applies only to when people are swarming you with maxed out armies, which in your kingdom hardly is the case. If you want to go on full defense, build a ranged army (With enough infirmary capacity) and upgrade your wall def + hp.
From personal experience, for the past 2 months I've been crazy on defense. Built up 200k troops on defense. Last KvK, an equally strong player attacked me with 250k troops, and they struggled taking down the wall (which they didn't succeed to in the first attack), causing them to lose 120k troops, with not any loss on my side.
I beg to God that you don't research any of your wall defense, while you're still approaching T4. Walls in this game are completely useless and I can probably take down anybody's wall without siege that's just how useless it is.
I expect to see your wall defense, and anything to do with walls lower than level 8 because otherwise you just wasted your time and resources. The main thing you should be focusing on is either ECONOMY, OR MILITARY period.
If you're a spender, then go ahead and start on your high research with Military Leadership, but if not I suggest you get Military and Economy to a decent level before starting to go past the phalanx's
Walls are not completely useless but they are the lowest in terms of priority for researching. If you are planning to get t4 as soon as possible then researching on walls will be a complete waste of time as you would need MAX ECONOMY and MILITARY.
However, the process of getting t4 is a very long and EXPENSIVE process. It would cost around 700,000 gems since you need to max all your buildings and it is recommended to max your treasure trove to earn more gems per month. It is because of this that people would normally invest in to monster hunting all the way down to hit level 4 monsters and the 4 researches after it.
I would recommend your research priority to be as follows:
1) Monster hunting
4) Army Leadership
Why monster hunting? Level 4 monster hunting gives me 5000-8000 gems a month, 12-15 days of speed ups every month, and maybe 3-8 relocators a month. If you get this as soon as possible then you actually save more time. Imagine... 12 free days for every month. You play 6 months and it's like your have a progression of 9 months because half of the time is free speed ups. Plus monsters give RSS packs.
Next, why military next? Let's face it. Your economic capabilities from your RSS buildings would suck at the early levels. It's faster to gather plus you should gather for materials anyways. Military will be your way to defend yourself or fight back. You can also burn castles for RSS which will give you much needed RSS instantly without using the ones in your bags. Plus researched troops will probably kill more on defense than your walls could ever do... And without the super slow downtime of your walls.
Next is economy since your RSS buildings should be better by then.
Army research is next because the phalanx formations will be extremely useful in killing enemies on defense and can decrease losses on offense. Plus we are getting this also because of the treasure trove deposits. If you get it to level 9, then you earn an extra 7000 gems per month from your trove... Always nice.
Next would probably be upgrade military since healing troops is quite expensive plus instant talent changes can help you go to war mode very quickly.
Then walls would probably dead last...
Don't worry about it.
All the above advice is really helpful, but there is so much to take in that it it can be overwhelming.
None of the consequences above will really matter until you get beyond castle level 10.
Your troops, resources, wall and leader will all heal or recover so fast at the lower levels that none of the above is much of a problem.