In the Voyager episode Relativity, Seven of Nine is recruited from the past to help catch Captain Braxton, who is planting a temporal bomb to destroy Voyager.
But there's a catch: After 3 jumps, (to the future and from the past I believe?) she will start to suffer from temporal psychosis. Why is this a problem? It's clear that only the future Seven of Nine would suffer temporal psychosis. For example, only the "future" unranked Braxton was suffering from temporal psychosis, not the "current" Captain Braxton.
So why would there be a worry about Seven of Nine getting temporal psychosis? If the past Seven of Nine dies, can't they recruit a new one each time?
Doesn't it just wipe the slate clean and they can have 3 more jumps with a new Seven of Nine?