I think i've heard something about most webcomics being cancelled within the first year or the first 30 pages or something? Because a lot of new webcomics are noobs (comic noobs, that is, not art or writing noobs) testing it out and then realizing it's an artform that takes a lot of effort and offers very little payback at first compared to many other options.
So if you want safer game, try to only read webcomics that have been going on either more than 1 year or 30 pages.
Another alternative is to try to stick to creators that do what they do for a living since they have a reputation to protect, and screwing that up might end up in them cooking cheeseburgers at McDonalds. If I were to cancel any of my 5 ongoing comics tomorrow, I would betray everyone's trust and a lot of people wouldn't believe I would finish the other ones either.
Perhaps you should consider reading premium comics or Webtoons exclusives, since those are financially backed up. It means the creator actually gets paid for their hours put into it, and that they have a contract that requires them to continue providing new updates. Sure, they could find a way to get out of that contract, but why would they? It's earning them money for time spent doing a project that is entirely theirs.
Alternatively you could check the creator's patreon page. If their main source of income is their webcomic, they're more likely to finish it.
If their patreon page barely has a mention of comics and is just full of illustration rewards, and the person is offering commissions, then their likeliness to finish the comic depends. Is it a longrunning premise? Then there's a risk they might drop it if financial crisis strikes, since commissions pay more and creators have bills to pay. It doesn't matter how much Sam loves his shark romance webcomic, because Mr Electrical Bill is a very mean man and Sam's tablet won't even turn on unless he pays him. So shark webcomic's gotta go.
If it's a short premise, it's likely the creator will finish it regardless of workload, and also even as a hobbyist. It will run slow depending on said other workload, but it's easier to wrap up and finish a short comic both in terms of story and drawing it to the last page.