When’s a few months, two? If so you should be fine. Phone them up close to renewal date line date and ask for an extension. Explain that you are having trouble getting the forms filled in. This will buy you a minimum 2 week extension*. So you should get to the trip before any decision is made on your claim. If you do not get motability award again I think you are allowed two weeks before car is handed back. Even say 1 week and the 2 week extension and by the time they do the actual assessment you should be back from the holiday.
* Don’t leave form to last minute, do it asap and sit on it a bit just to buy you a bit of time.