How long can you keep a rupture saline implant before replacing them?

Although there is no urgency to removal/replacement of the ruptured saline breast implant, waiting for a prolonged period of time may lead to additional work necessary during the procedure to “reopen” the breast implant pocket, that tends to contract down over the deflated saline implant. Therefore, probably best to have the procedure done within a month of deflation, if possible. The advice above is quite general; you will do best seeking consultation with well experienced board-certified plastic surgeons in your area. Best wishes.

Forever I guess it an answer but keeping a foreign body without a purpose is not recommended especially as it is so simple to remove it. I generally do it as an office procedure under local anesthesia.

You may keep the ruptured implant for life.  However, as it collapses, you may notice more corners and points.  These can become quite irritating. Your implant can just be removed under local anesthesia in the office.  However, if you wish to replace it, I would suggest doing so before your scar tissue lining collapses around the empty bag.