You could run it until it completely dies.
Keep MDI for backup. Should your old pump actually have complete failure, then immediately switch to MDI while you then decide which pump. Potentially the options available and/or the features on the pumps available and/or company policies may have changed during the extended running of your out-of-warranty pump such that your ultimate decision may be different.
This was our plan while on the Animas Ping when the warranty expired. At that point in time, we were just not comfortable making any decision so we continued to run the Animas Ping with support but without warranty. If the pump died then we would immediately switch to MDI. We did that for two years. At that point, we did come to a decision about which pump to switch to prior to the Animas Ping completely failing.