[imranq]

Sorry I’m not quite following. I understand if groups are isolated from each other we will have different forks of Bitcoin running around the world, but why would a fork disappear? Wouldn’t the separate partitions merge into one network again?

[xxbondsxx]

The forks don't "disappear", but they get overruled since the consensus has shifted to the majority opinion of the ledger. Thus all of the transactions on a local fork (that doesn't become the majority) are wiped out -- including possibly deposits in exchange for cash.

[pjkundert]

Surprise!

Nope. Correct behaviour is that the longest chain “wins”; all others disappear along with all their transactions.