this post feels like propoganda. prior bitcoin upgrades have gone much smoother and when they do go wrong the community banded together to spread the right information. albiet the userbase was likely a lot smaller back then.
If the soft fork fails, Core developer Luke-Jr said they'd change the Proof of Work algorithm and possibly create an altcoin (or bitcoin if enough follow).
This is like a Russian Roullete situation. The gun's loaded, all signs point to neither side conceding. It's the cypherpunks vs the corporate miners (plus some former devs and very credible people).
There are three factions here-- Segwit2X and Core, who both want segwit, and Bitmain which does not want segwit and which has threatened a forcible hard fork into a bitcoin that has unlimited block size-- and they are even talking about doing an ICO and things like that:
https://blog.bitmain.com/en/uahf-contingency-plan-uasf-bip14...
And Luke's subsequent comment said if enough followed then it could still be called bitcoin.
Also Maxwell said he'd quit if BIP148 fails. If the soft fork fails, bitcoin will be something different.
That said- this is a legit notice and is probably good advice. This is a contentious upgrade.
The Segwit2X and Core factions agree on Segwit. Core doesn't like later doing a 2MB hard fork, but most of us think it's a reasonable compromise. There won't be a lot of complaining.
The real threat is Bitmain which wants to do its own hard fork, that will NOT be compatible with Segwit, which they intend to mine privately and which will have unlimited block size:
https://blog.bitmain.com/en/uahf-contingency-plan-uasf-bip14...
That's what the original post is about. That fork is very dangerous.