I would not go to CRL and spend the evening in a massive line trying to get a voucher for a poor hotel. If it is important for you to be in the UK that day, then book an alternative if you can. Note that there appears to be a strike of the railways in Belgium on July 12-14 so going to AMS might not be straightforward.

When FR cancels your flight you can request a refund of the original ticket and try to claim your expenses back, that might of course be a battle.