Is this a mandatory swap or could the coin holders keep their old pop coins?
Yes, it is a mandatory Swap.
The Old chain will be forked for the long run and all coins swapped will be held by dev until the swap is concluded (Probably about two years total) and then the coins will either be burned, or whatever the users would prefer to do with them.
Before the Swap we will publish detailed steps to take in order to ensure that your Popular Coins are safe and that you are ensured in case someone whats to continue the old chain or anything along those lines. If someone wanted to continue the old chain they would have to rebrand the Ticker and Coin Name, Root Folder (Not POPCOIN) and create their own repo, but they technically could do it and everyone that has POP would have some on that chain too,..
The New Github repositories that will exist on Pop Currency Foundation:
one new repo for the old chain after we fork it (will be title Popular Coin Classic most likely)
and then the current Github repo will get the new chain installed to make it simple, no one will have to change links to the source code
Let us know if you have any other questions.