what happens if you hold x amount of a stable coin in one of the many lending crypto platforms available (crypto.com, youhodler, nexo, etc)
Stable coins are
and that coin fails and goes Kaput? Do you loose it all? or are your assets moved to another token or FIAT?
It depends. As consequences from their inflation schedules, their values can fall to lower than $1 for 1 stablecoin (1 USDT, ie.) or to zero.
Initial stable coin can be swapped to another stable coin or another token, if the company want and still be enable to do so (without lawsuit or prison charge from governments).
Whatever the scenario is, any of which will be terrible.