There is no current alternative to replace Bitcoin and that is because Bitcoin hasn't failed yet. There are several hundred coins lined up to try take that position though if Bitcoin ever does fail. The crypto economy can survive without Bitcoin but I think a lot of confidence would be lost at that time, although a recovery to me would seem inevitable.
I agree that there isn't any replacement for it now because it's the very first kind of technology for its function. However, since we're talking about surviving, then I could say we can. We have survived without it before, and so, we can even when it's gone. But, the thing is, it's hard to go back to our old ways in this every changing world. Technology is made to make lives easier and more efficient for those who can use it. Bitcoin, or in general, cryptocurrencies is one of those things that make it easier for us, that's why it's difficult to be way from it, especially if you have been used to using it.