What if for example, 10 witnesses don't vote at all? What will happen?
I think the only solution is to vote new witnesses in. Or wait for enough rounds to get the votes from backup witnesses.
I think it's not just related to OBI and is the same for the current design too. Assume 10 witnesses miss the blocks and don't produce anything for a while. Since it requires 15 different witnesses to vote for irreversibility by producing a block.

Do you think a built-in failover mechanism is needed here?