I'm optimistic about bitcoin in the long run and like many people on here I have my own personal reasons for WANTING bitcoin to succeed.

With that said,  yes there are plenty of times I think about bitcoin failing over time.  I believe p2p cryptocurrencies and the technology behind it is certainly here to stay.  Bitcoin itself very well could die off in the future,  but cryptocurrencies in general are certainly here to stay in one form or another.