Hi Brent,
I work on surveys from different computers.
When I'm finished on one machine, and I'm happy for the changes to go to ArcGIS Online, I published them. When I'm on a different machine, I sign into my account through Survey123 Connect and download the updated survey from there.
If I'm not happy for the changes to go to Online, I take a copy of the survey folder from C:\Users\<username>\ArcGIS\My Survey Designs, email it to myself, and then place the folder in the same location on my other machine.
I haven't collaborated on a survey with anyone, but I have been able to transfer a survey to someone else by creating a folder in their My Content with the same name as mine, and changing the ownership of the survey to them.