Wow, your friend broke it, and instead of demanding the money to pay for its replacement, you're saving up yourself for a new one? What a forgiving friend you are. Can I borrow your new bass head when you get it? =P
As for long term, meh. It'd be cool if you were using a dual amp setup with the guitar amp taking over the higher frequencies, with a nice fuzz perhaps. But I think you'll suffer a fair bit in the low end using only a guitar amp. If you say you already have the guitar amp, go try it out, and see how you like the sound of it.
As for buying a new guitar amp... Well first, I really think that depends if you really want to play with a guitar amp for your bass. If you haven't tried that oit yet, like suggested, then don't even think about it. Go try it out. For most bassists, you're really going to get more versatility from a bass amp though. If you want to sound like a guitar amp after that, use your EQ to cut all the super low bass frequencies right out.