what I don't like about tendermint:
"If the validator causes the blockchain to fork while its coins are locked in bond, all of its coins are destroyed."
so if the developers make some mistakes, or I have some network problems or whatever and it forks, I loose the coins. Wow!
I didnt like it (yet?), but I think this specific issue you raise is fine: only a validator loses its own bond when they fail to function whatsoever.
even if it's not their fault... that's what I don't like :-)
getting into a fork can be very easy with PoS: with a poor connection and some stake you can easily generate orphans and get them accepted by your neighbours.