Hi Linda,
This is all with the assumption that Instructurecon 2019 is still at Keystone - it's possible it gets moved and they likely won't announce it for a few months.
I did InstructureCon 2 years ago with a stroller, so it's not directly applicable but hopefully useful info. The main conference rooms are at two locations, both of which have shuttle buses from the various hotel areas. As long as you leave yourself time to catch the shuttle bus (which come by every 5-10 minutes) a scooter may not be necessary. However, the conference hall areas themselves are rather large, but flat, with an elevator to get to the second floor area, so a scooter may be useful there. I honestly can't recall if the shuttle bus was equipped to onboard a scooter.
In general, the outside area is a bit "hilly" - plenty of cart paths, and there's almost always golfcarts running around to get people to where they need to go. The main "lunch" area is on woodchips, which was a problem for our stroller, but last year they had some workarounds (if I remember correctly - there was a rubber mat and also employees willing to bring the food to you). I know after our experience with the stroller and at least one other person with a wheelchair, they worked on making things better and more accessible - but there still is a lot of distance between locations.
Hope that helps.