Just to let you know you're not allowed to sell the mayor title(or any other rank) in your town; you're allowed to give it to someone else for free (as long as they agree to the town application rules), but cannot receive anything for doing so.
Also you cannot guarantee yourself a permanent position as co-mayor, the mayor in your town has overall control and is allowed to add/remove staff as they wish (as long as they're not selling ranks), if you make someone mayor they will have more control than you and could therefore remove your rank if they wanted to.
If you're unable to find a new mayor please contact me and I'll look into options for you.