Dear Rabbi Simon.
We are selling our house when we make Aliyah. Our buyers are religious and went as far so as to request a Heter Iska be included in the Contract.
My question is what is my obligation re: leaving Mezuzot given that the purchasers are Jewish (and in fact frum)?
Strictly speaking you must leave your mezuzot behind. It is improper to leave a home without mezuzot (unless you know or presume that the new residents are not Jewish; not applicable in your case, as you explained). You may take the mezuzah cases if you like, but the scrolls themselves should remain. However if the purchaser prefers his own mezuzot, he may certainly replace yours with his and give them to you. You may also charge him fair market value for them—which may motivate him to say, “take yours; I’ll install my own.” However even with his permission you may not leave the house without mezuzot. He can send them to you when he puts up his own, or he may do so before you leave and you take your mezuzot with you.
I hope this is clear enough.
Rabbi Rashi Simon