Question: If a person forgot to say al netilas yodayim until after he dried his hands, has he lost the brocho, or can he still say the brocho?
Answer: Ideally, one is supposed to recite the brocho of al netilas yodayim before one dries his hands (c.f. Remo Orach Chayim Siman 158 Se’if 11) since drying the hands is also part of the mitzva of netilas yodayim (therefore it is still considered “over l’asiyoson” “prior to performing the mitzva”).
According to the Remo (ibid) if one already dried his hands he can still recite the brocho. The Taz (s.k. 12) however maintains that one cannot recite a brocho after drying his hands.
The conclusion of the Mishna Berura (s.k. 44) is that one should avoid this scenario [i.e. ensure to recite a brocho before drying his hands] but ex post facto one should follow the opinion of the Remo and recite a brocho even after drying his hands.