I would first check if you can keep it onboard. If not and it has to be checked, then it would be covered by the same limited responsibility as any other checked item, which means that the value the airline can be responsible for is actually extremely low.

If, as I suspect, your rollator is a relatively expensive item and you find that you cannot (or do not want to) take it onboard, then you should insure it (can be done at check in) if you want to be sure that it would be appropriately compensated for should it be broken during the trip.