The best thing you can do is backup your Jaxx wallet's seed words. Jaxx uses a system where it can generate an almost limitless number of addresses (and private keys) from its seed words. If you only back up the private keys your wallet currently contains it may generate more, then crash. You risk losing coins in that situation if you didn't back up the seed words.

If you have the seed words for Bitcoin addresses you can import them into an alternative wallet like mycelium which will restore access to your coins. I advised someone who had a malfunctioning Jaxx wallet to try importing into mycelium some time ago and it worked. You can read about it here.