dnd 5e – Party divided in two: how do I gather them?

I have a 4 player party.

In the last session, a player could not attend. Although I felt uncomfortable playing a game without another player (I have done this in the past), all the other players insisted a lot on playing, including the absent player.
The players were in prison. I put the absent player in solitary confinement for contraband that he had requested in the previous session. My other players in prison were chosen to participate in a skills challenge that really killed them both.

At this point, 2 players are dead, 1 player is not in prison, 1 player is in solitary confinement.

At this point I considered ending the session. My other two players already had new characters and they were excited to play them. With time, we start again. My three players at the table stayed away from the prison; only one had some kind of reason to stay near the prison and try to bring down the last one.

I have cornered myself and I need help. It's been the first game I've played (if it's not too obvious) and I'm having a hard time figuring out how to defeat the last player.
My other 3 party members are quite far from prison at this time.

The party: bard, school of swords; Fighter; Ranger; Arcane Trickster Rogue in prison. Prison suppresses magic. The three who are out of prison are about to enter a dwarf city with missions there.

Should I have someone to take out the last one but offer a search as a way to pay the debt?
Should I have him acquitted?
Should I have downtime for all the players so that the sentence is fulfilled (2 years)?
The best way to rejoin the party would solve my problem.