I think that is a very good question and not so hypothetical. Not likely in the free world, but I’m sure there are parts of the world and specific situations in repressive countries where Catholics are physically stuck an may never receive the Eucharist again. There may be children being secretly raised Catholic in repressive countries who will never receive the Eucharist.
Imagine being a Catholic in N. Korea! Yes, there is a North Korean Catholic Church, but it is not under the Pope, but the Communist central government. All the legitimate Catholic clergy “disappeared” many years ago. They do not celebrate Mass, so there is no Eucharist, legitimate or illegitimate. There are still estimated be 3,000 surviving Catholics there.