Honest question: do you agree with the estimation that the more time lapses and bitcoin continues to develop and entrench itself, the less likely it is to outright fail?
Well, first, I doubt that it is actually "developing" and "entrenching itself". There are many companies that need it to survive, and several hundred millions available for marketing and PR efforts (like the St. Petersburg Bowl, fat discounts for bitcoin purchases, slots on Bloomberg, etc.). However, the few minimally reliable and meaningful data about adoption do not show that it is growing, and hint that it may be decreasing.
Second, the failure modes that I can imagine are not going to be detectable in advance. A killer bug may surface, a much better remote payment method may arise, the price may drop further (even if there will be another bubble or two before that) causing most of the miners to stop, there may be a successful majority miner attack, the US may ban it, etc. More likely, competition from other digital payment systems will cause the user base to shrink.
Bitcoin's economic structure is unsustainable because mining is being supported by new investors (to the tune of 800'000 USD/day) instead of its users; and there is no plausible roadmap to fix that situation that will not go through a price and network collapse. Moreover, the radical "free market" system that is supposed to define the transaction fees in that post-reward era, with unpredictable fees and no service guarantee, cannot possibly work. Because of the mirage of "deflationary currency", its price is 90% o more due to speculation, rather than use as currency. The huge and unpredictable price swings are a consequence of that. And so on.
Another possible outcome is a mining cartel taking over and becoming a de facto central authority, with power to change the protocol, set minimum fees, cancel transactions and seize funds, etc.. Believers have convinced themselves that such takeover is impossible because the "economic majority" has control. I have looked into those arguments and I believe thay are just wishful thinking. The only choice that the "economic majority" will have is to accept the cartel's takeover (and tell everybody that it is actually "good for bitcoin", hoping that the coin will not lose much value), or to lose everything. If that happens, perhaps bitcoin will continue to exist, and will continue to be used as a speculative intrument (as it is in China) and/or as a payment system. However, if it becomes centralized, it would have failed in its goal.