Leaver penalties have changed significantly in the past year.
There was a decrease in the amount of time it takes for someone to get a season ban, the AFK timer has been adjusted, participation-based game ending was introduced(if someone leaves within the first min of a match but they do ANY damage or healing the match won’t end), and more importantly you’ll almost always be given a suspension if you’re gone from a match for any sufficient amount of time.
In your case if you’re gone longer than a minute or two it’s probably best to just forfeit that match and “gg next” as the kids say. You can go back and play if you want, might even win, but it won’t be for your sake.
and yes, you lose SR on all roles(-50 for that role, -10 for others) if you get a suspension.
The whole system has been made more punishing because leavers and AFK have been a very annoying problem.
This is my research on the new leaver penalties:
Wyoming Myst confirmed the changes to the leaver situation but I can’t be bothered to find the post in their billion or so other replies since then, so please take my word for it.