... what would/will be the next most promising smart contract platform for the eth-based projects to migrate to?
You can replace your money into another coin, there's a lot of coins to make profit besides eth. For me monero, ltc and ripple is a good investment after eth. Besides that, coins can dies is part of risk so let's deal with it. See again your strategy and looks carefully, if you think that coin will dies, just leave it. Good luck.