There is a one year time gap in the first season of Critical Role, after the dragons and before Vecna. It was handled well.
The DM took the players aside and asked them each what they wanted to do with that year, and then let the characters quickly speed through the year. Then they all came together and shared their years collectively before picking up the action.
When I've had prolonged downtime, the usual activities for PCs have been magic item creation, forming their own guild, colonizing, public service, starting a family, and building a facility (mage tower, church, etc...)