Why couldn't you just set up 3 rules:
1. rule after 30 days: Hey, we miss you
2. rule after 60 days: Hey, not sure if you missed the first email which we sent you 30 days ago,.. get back to us.. If you don't get back in the next 30 days we'll delete your account.
3. rule after 90 days: account deletion.
And to avoid any issues, I would probably create rule 1 today, rule 2 in 29 days and rule 3 ( deletion ) in 90 days.