I totaled my 2008 Civic Hybrid, Is it worth it to buy it back for $4k?

If the Insurance company pays you the full tab - then they feel it is a TOTAL LOSS, and so should you! If you buy it back for the $4500 - you won't be able to fix it and re-sell EVER - and it would not pay to part out the car for the good pieces, unless you have already priced the parts and they equal more than 4500 (your cost) - actually - its a bad investment.