Splinterland assets are not at risk. That is a layer 2 solution, hence they only post to Steem using custom JSON. This could continue or be directed to the new chain, it really matters little from the user perspective. All trading of the cards also occurs off chain with a notation made to the blockchain of the transaction.

The same goes true for all other applications. They will decide where they go. Some, like Dlease, already determined to support both chains.

As for the money you invested into STEEM, we will get details on the airdrop but I believe it is a 1 for 1 drop. Thus, you will still have your STEEM plus an equal amount of the new token.

It is likely that there will still be part of the community that remains on the old chain. IN my mind, it is going to come down to the apps that people use. If Splinterlands is posting its transactions to the new chain, then that is where users of that game are posting. But than again, does it really matter to the end user?