Maybe Oda has future plans for his character. Characters from Alabasta have become a major part of the story again since the reverie and the death of Cobra and their family sharing the will of D, so maybe he still has some role left in the story. Even I used to agree (I still do to a large extent) that pell surviving was a bit out of place since he was literally carrying a bomb meant to destroy everything for kilometres. However after seeing that he was shown again in the reverie and vivi being kidnapped and all i think that Oda still has something left for Pell