Can deflated saline implants be safely left inside the breast once all fluid has been drained?

Yes I have heard of this technique but I dont do it.  I prefer to remove the implant if it is deflated.

If the idea is to leave them in for a short period of time while your tissue contracts around the implant to later have either an exchange or lift then the answer is it will probably be ok. But I have seen three case where doctors left them in for years deflated and the patients eventually developed so much scar tissue that it became very painful which then lead them to come in and have them removed. So typically we would take them out.