I made 90% of a game several years ago, or lets call it a rather large demo. I came back to it to finish it a few years later and an update killed parts of my roaming NPCs for what ever reason, assume code strings and such. I am afraid if I upgrade again, more of the game will be cut and I will have to restart basically from scratch. If I complete my game using an older version of Quest and then publish it, can anyone play it or only those using the older version?
Also how does a downloaded Quest differ from the online browser kind? Pros and Cons? Can one be played in the other format without errors?
You can use the older version to publish, and that's what I'd suggest. You are probably right about an update causing problems, and Quest is backwards compatible back to 4.5 (I think, but it may go all the way back to 1.0).
The online version of the Quest editor sucks compared to the Windows desktop version.
Games made online will play in the desktop version, and vice versa.
The current version is 5.8. Games created in 5.8 will not play in previous versions of Quest, but 5.8 will load any game (new or old).
You can play any (earlier) version of Quest.
If you try to edit a game created in an earlier version, Quest will save it as the new version. That generally should be fine. These was an issue around 5.3 where the way string lists were saved was changed, and the next version could cope with both, converting to the new way, but the version after that choked on the old version. I am not aware of any other issues.
I would suggest making a back-up, then opening your game in the latest version, make a minor change, save it, then check it plays. If it fails (and it is not trivial to fix), go back to the backup, and use the original version:
if you open the file up in a text editor (eg Notepad), the first line will tell you what version of Quest it was written in.
That said, if your game was written in version 4, you will not be able to open it in a Quest 5 editor. Versions 1 to 4 are not at all compatible with version 5 editor (Quest desktop has three parts, an editor for Quest 5 games, a player for Quest 5 games, a player for Quest 1-4 games).
Mine says Quest 5.7.6606.27193, but that was probably AFTER I had already tried to rework it. And asl version="550" what ever that means. So the new Quest will basically play any version of Quest games. But in order to edit a game it has to be of a certain newer version?
Good god... my original profile name and thus when I started to use Quest was back in 2012... o_O I should have several games by now published. Where the hell did the time go!?