I had something similar happen recently, my bank website authentication going out for four days (it was part of an upgrade that went bad).
That's pretty much unthinkable these days. It really made me think, if that's even possible it may be a good idea to abandon this bank for some other.
Would other people give a service a one time pass for a multi-day outage if they otherwise liked the service? Or should that be a flag to drop them, any time it occurs? If the criteria you use to leave a service is too strict, you may be switching often...
Things break unexpectedly - whilst it shouldn't happen, it does and so long as it doesn't happen frequently and the vendor is reasonably proactive I'd generally give them a pass (for one thing, moving a bank account or similar is probably more hassle than a one-off outage). If it keeps happening then yes, I'd move to a vendor that has historically shown to be able to run a more reliable service.
However, one thing that I think is unforgivable is when the vendor doesn't bother to actually keep their customers informed. A single "the service is down, sorry" post which doesn't give any ETA, progress updates or anything just isn't good enough. Tell the customer what's going on! It seems to be all too common to keep the customer as uninformed as possible these days, especially with the larger companies. I imagine it's a combination of PR damage mitigation and liability concerns, but its just not helpful to the customers - I'm much happier to give my business to a company who says "oops, sorry, we screwed up, here's what went wrong, but we've now investigated and put measures in place to make sure it doesn't happen again" than a company who has an unexplained outage and doesn't provide any information about it.
I'll give an example - back in the 90s I had my internet connection from a small ISP called Demon Internet. They were pretty good - the techies knew what they were doing and they gave regular status updates. If something went wrong, they would publish it. If an outage was caused by someone screwing up then they'd let everyone know, even if it's a stupid "oops we unplugged the wrong cable". Then they got bought by Thus, a much bigger company, and the "big company" mentality very quickly showed - the techies stopped talking to the customers, status updates rarely happened and they especially never admitted that they'd made a mistake. I wasted hours on several occasions debugging my CPE because they swore blind they had no network problems so it must be my end before it became very apparent that they did know about problems in their network and they were just trying to keep it quiet. And that is why I dropped them - I'm not interested in dealing with businesses that waste my time by covering up their problems and refusing to keep their customers informed.
WRT services like MyCloud, I do wonder what kind of terms & conditions they give the end user, given that this is essentially a paid-for service. If they provide absolutely no service guarantees and can shut it all down on a whim then clearly it isn't worth paying for.