This may be a very naive suggestion, but could ETH deposits for ETH2 validation not be reflected in bETH, but only generate bETH rewards which are frozen until a migration phase?
ETH could even be withdrawn from deposits, but in doing so, could wipe bETH earned by that deposit.
This would create a deposit incentive that grows as bETH rewards grow, but could make ETH deposit recovery effortless in the case of failures.