Will some of them disappear due to not getting paid? In which case the sig ban is good enough, as it gives good users a second chance and effectively bans the financially-motivated ones. Will they abuse the sig ban? Not sure how they would do that though.
I believe most of them will less active although they will not disappear fully. Extend tepm ban without signature ban could not prove "contribution" of banned user. I think that is not easy task to abuse signature ban due to merit system. No one could easily skip it, they have to earn merit if they want to abuse ban but likely they will not able to do it. For example almost need a year to become Sr. member and need merit as well.
Overall I think current ban system is enough fine. They should say thanks to theymos that they are not banned permanently.