You have chosen savings over comfort/de-risking, which I can totally understand.

In addition to the best advice above (asking the airline to 'protect the return' which in my limited experience they will do) I would add that if irrops happen, then is the time to throw cash at it and sort it out later. That's what your credit card is for. As long as you have been reasonable - for example, renting the cheapest car at their partner Avis in LHR rather than the X5 you are used to - you will rarely be questioned on asking for reimbursement.