It's not reasonable to go toward unknown territories when your ship is as vulnerable as that, the next ship that shoots a popgun at them could very well tear the hull apart. But whoever said that Janeway was reasonable, right?
After looking at the transcript of the episode, it says the ship wasn't horribly damaged. The Kazon themselves didn't want to damage the ship much because they wanted to use it.
Tom's plan involved overloading the phasers:
PARIS [on monitor]: Doc, I hope you're receiving this because if you're not, I'm a dead duck. I'm piggybacking this message on a fake Kazon signal I'm sending to the Bridge. I'm betting they won't be monitoring your Emergency Medical channel. I'm bringing help, but you have to do something for us. When the attack begins, I need you to get the computer to block the discharge from the backup phaser power couplings. You got that? The backup couplings. I'm taking out the primary couplings myself, but I need those backups to overload when they switch to them. Don't do anything until the attack begins or they might notice. That's it for now. I'll be seeing you soon. I hope
They also said that backup systems were still onilne:
KAZON ENGINEER: Primary phaser power is down.
SESKA: Switch to backup systems.
KAZON ENGINEER: Confirmed. Phasers are locked on.
after that the phasers overload.
After that Tom and the Talaxians beam to the ship, Tom starts working on some issues:
PARIS: I'm sealing off the Bridge manually. I've got to get the computer back online. All Starfleet voice access has been disabled.
PAXIM: I'm reading a Kazon shuttle leaving the ship. There are also escape pods being launched.
PARIS: Forget them. We have more important things to do.
When Janeway comes back on the bridge, Tom tells her what they did:
PARIS: Welcome back, Captain.
JANEWAY: Well done, Lieutenant.
PARIS: I had a lot of help. The Talaxians, the Doc, Mister Suder.
KIM: Suder? We thought he was killed during the initial attack.
PARIS: No, he and the Doctor sabotaged the ship. Suder disabled the phasers before they killed him.
so shields are damaged but not completely down, phasers are overloaded. Other than that pretty much everything else is working. There's no reason they couldn't warp away and make those repairs.