so if a user gets 30 up votes on his answer today, he can only get 200
points today. But what about the rest 100 points, will he get 100
points tomorrow or 100 points are gone for good?
Gone for good. But note that this has nothing to do with the tag score, you'll still get 30 regardless of the reputation.
Also it's not exactly correct that the max reputation is 200 per day, you can reach more if you have an accepted answer or won a bounty..
It doesn't make sense to earn 200 points today, and 100 tomorrow. If that's the case, then why not winning the 300 points today?..
faq. Everything you need to know is pretty much already present there.