Maintaining the app and not moving forward with new features and adding value (because of lack of resources), I would assume it would just die eventually.
Doubly so when a brand reaches infrastructure level - like Github, or arguably Dropbox. Just don't screw with the product that's working well. Not breaking things isn't expensive.
It's the corpse model of product development.
Looks like your sentence is incomplete.
That, ironically, makes me REALLY not want them to go under: they don't deserve to.
The problems are issues, code comments, pull request discussions, etc, which may be harder, and their API helps here.
Github's huge win is the network effect of having one account and being able to interact on thousands of issue trackers, create PRs, etc. It would super cool if GitLab could achieve some of that same experience without requiring everyone to all be on gitlab.com. It would go a long way toward addressing the criticisms that Github is too centralized.
Yeah, I think it'd be awesome if there was some form of optional federation between GitLab instances (sort of like Matrix or NextCloud).
I also recommend to check out Gitea (community fork of Gogs) if you haven't yet, it's a nice alternative to Gitlab for selfhosting.
It seems like other smaller companies have exploited the profitable parts of Github's niche out from under them.
I think I here a bell tolling.
Maybe I'm too nice to them, but that doesn't seem like Microsoft's modus operandi anymore. These days they're all about getting people to buy more CPU cycles from Azure, rather than trying to seriously pursue Windows platform lock-in (which is a lost cause and they know it).
I imagine if Microsoft did buy GitHub, they'd have all kinds of offers like "get automated tests and CI to your Azure machines every time you push", or allowing you to host the repo on your own Azure VMs but still use the GitHub interface, stuff like that. They'd probably keep the free GitHub mostly as it is, with some nagging to upsell premium Azure stuff but nothing worse than that.
As for Google, I agree that they tend to get easily distracted and drop things, but I would hope that GitHub is popular enough (both inside and outside Google) that there would be serious pressure not to let it die on the vine. Contrast with abandonware like Wave and Google+ which never got enough mindshare that anyone felt like really fighting for it.
Supposedly competitors may be cheaper or offer more in the free tier, and I could imagine you'd call Git itself a 'misstep', but otherwise I can only think of incredible cultural and technical achievements by GitHub?
That being said, the product itself is stellar.
I'll take Oracle, SalesForce, or Microsoft over Google any day of the week. The worst Oracle will do is start charging me more, but god only knows what kind of sleazy ad tracking Google will add. No thank you, I'll move everything over to BitBucket.
Fortunately, I don't think Google will bother. They already shutdown Google Code when they couldn't use it to increase ad revenue, so hopefully they'll leave GitHub alone.