I was in exactly this situation once - but the other way round. The company wanted us all to move from a cheap residential area to London. They offered outer-London weighting, and a very little help with extra mortgage costs, but they knew ( and clearly intended) that only the young, single people would be able to move. People with family ties, children in school, etc were obviously not going to be able to up-sticks and move. So we were declared to have made ourselves redundant if we couldn't accept the offer.
Eventually, though, they did have to shell out full redundancy money, though even then we were tied to staying until the very last day . Anyone who left before the last day had their redundancy money reduced proportionately, so only those who managed to find new jobs quickly could afford to go early.