What do I do now so that when the platform doesn't work, I still can?
Now the answer is obvious: you don't need to stop using platforms, you need to stop being dependent on any given platform.
Store all your videos in two different storage providers, plus your house archive. Have accounts on at least two different video distribution systems. Get people interested in seeing your own website regularly, so they don't just subscribe on one platform and ignore you otherwise. Get them engaged in several communities. Occasionally put special bits on just one of those video distributors, and then add them to the other(s) later. Get people used to following you.
This is, obviously, more work than just shoving everything to a Youtube channel, or just posting to Medium, or just hosting with Wordpress -- but the point is that when one of them folds, has a service disruption, declines your credit card, or is invaded by leet script kidz, your business survives and merely suffers from hiccups while you re-point things.
if you are 21 y.o. vlogger focused on barbell training and restoring old american muscle cars, this advice will sound like "dude just do more straight deadlifts and focus on hi-rep kroc rows, they will help you with development of your back" -- aka, some special gibberish speak. it takes so much knowledge to do so, it just won't happen.
Sometimes, they don't want to.
Sometimes, they would rather not.
Sometimes, they would rather pay more money or spend less effort.
I would guess that your hypothetical vlogger is likely to just open a Youtube channel and pray, and they will get results consistent with that. It's not a business plan, and they didn't ask my advice.
If you see a business opportunity in making these things comprehensible or easier or more affordable to vloggers, you should go ahead and do that.