Tippero tips are non reclaimable. When tipping, an account is created for the recipient in Tippero's database if one did not exist already, and the tip amount is moved. There is no record made of past tips/rains/etc, so when given a balance for a given account, there is no way to tell where the monero came from (deposit, blackjack wins, tips, or otherwise).
Setting a time limit for tips is not an easy thing, due to the fact that Monero is fungible. What happens if someone tips Alice, and Alice uses her account every month playing dice, but never withdraws any ? If Alice's balance never falls below the tip amount, was the tip ever used ?
Monero does not support multisig yet, and there is no intention to support multisig in Tippero. This would require having a wallet per user, which would be very heavy. In particular, it would require tips to be actual blockchain transactions. When you consider than many tips are for very small amounts, you see that a sizeable portion of tips would end up as transactions fees, making the whole thing unworkable.
If Tippero winds down at some point, I expect people will be asked to withdraw their coins, with anything not withdrawn after some time being left for the dev fund.