Cats: what to do if we go abroad?

We have two cats, one 8 yrs and one 9 yrs old. We are planning on moving abroad, to Italy, at some point in the future (probably 4 or 5 years). We are concerned about what to do with our cats. Do we put them through the stress of such a long move (presumably by air)? Would they be sedated by a vet? Or do we leave them with someone, probably until they die?