There's two kinds of failed final glides:

1. Pilot continues until out of options and puts glider into bad place - or botches low approach at fixated destination.

2. Pilot decides insufficient margin and either selects good field or heads to landable terrain that can be reached at height allowing field selection and acceptable circuit.

With sustainers it's more complicated and we are learning that remaining battery capacity can be uncertain. The gas powered folks have long had their problems.

If you have a sustainer or SL, and are uncertain whether it will get you all the way back, you might want to consider climbing until the fuel or volts are depleted and then seeing where you can get from that height.