I’ve had two no fault accidents since joining MB in 2008 so no expense to MB insurers and both times i only had the hire car two week, one was a carbon copy of the actual MB car in for repair even down to the exact same hoist in the back. The other time I was given a car that I can only describe as coming from a company called “Rent-a-Wreck”, it was 4 years old and still had body repair dust in the engine compartment from a repair, that or it been used as a druggie car.
I don’t know how long they’d keep you in a hire car for but more is the problem of getting a car that is as suitable as the one you have, more important if you have adaptions fitted to your MB car as well.
The supply of car parts is a problem for everyone not just MB cars though a year is stretching it a bit.