If the Selected SGW Fails, Which SGW/PGW Will MME Select

If the selected SGW fails, which SGW/PGW will MME select if 'gateway selection mode 2' is used?

A) A new SGW, but new PGW selection is not required
B) A new SGW first, then select a new PGW that is topologically closest to the newly selected SGW
C) A new SGW first, then select a new PGW with the best order and preference values
D) The next topologically closest SGW/PGW pair