If they are moving locally, you could politely say no for the reason you've given us, that it's a wrench leaving your old garden, & the new garden is very important to you (and legally the plants will be yours)
Then take some cuttings yourself that you can offer them once they've established.
Plants can be expensive, & the previous gardeners would probably prefer their garden to stay as it is & be looked after by another knowledgeable gardener.