Just keep running from battles until you get back to Elfland with whoever is left of your party. You can visit the church/clinic to revive party members there. The Marsh Cave is pretty nasty and you will need a lot of potions and antidotes to get through it. I recommend about 30 each if you are having trouble. You may also want to upgrade your Fighters gear with whatever is available in Elfland and Pravoka. I also recommend teaching your Black Mage Thundara as well cause their is a nasty set of enemies guarding the Crown at the bottom of the Marsh Cave and it's the only element that they don't resist.

If you need to, there is a tiny peninsula northeast from Pravoka that has some high level monsters as random encounters. If you teach your Black Mage Fira, They can wipe out these enemies in about two spell casts and net you a ton of Exp. and Gil for this point of the game.