I rented a house from a frum owner for a year (because we were doing construction on our home).
1) There were no mezuzos when we got there.
2) When the construction was over we left the rented house. There were no new renters moving in to the house when we left (in all probability it will be rented to frum renters).
3) Our sofer told us that because there were no new renters moving in at the time we were moving out, we could therefore take our mezuzos with us. (When new renters would eventually come, we were told that we should offer to put up cheap mezuzos.)
4) As of today no one is in the rental home (in fact, the owners may move back in themselves).
5) We were then told that the sofer made a mistake, and that we should now at least put a cheaper mezuzah on the front door.
What are general guidelines of a renter having to leave behind mezuzos?
In my specific case did I do enough by putting back a mezuzah on the front door, or do I have to go back and put mezuzos on all the doorways in the now empty house?
There is an obligation on a renter to leave mezuzos on the doors of the house he rented after he leaves. This obligation includes all the doors of the house, and you should replace (cheap) mezuzos on all the doors. The owner of the house should pay you for the expense, but if he is unwilling to pay, you cannot extract the payment from his be means of beis din. However, if you still owe money for rental payments, you can the cost of the mezuzos from the rental debt.
Sources: Shulchan Aruch, Yoreh De’ah 291:2. Although Rema writes that the owner of the house is obligated to pay, this point is disputed among rishonim and later authorities, and therefore the renter can withhold rental payment correponding to the sum he paid, but is unable to extract the money from the owner of the house in beis din.