It's possible for a hard fork to increase Bitcoin's supply. It will NEVER EVER happen, nobody wants it.
The supply is projected to end in 2140, not 2021 (in case you're confused). At which point more fractions will be added to account for the substantially increased value, that is very easy to do.
If a Satoshi has a value of $1, a sub-satoshi could easily be added, having a value of $0.10.
As we heard from the expers, there is a code in bitcoin which prevents this from happening. I'm not sure if it's correct, but I don't think bitcoin developers will do this. A pump in bitcoin total supply would result in tragedy.