Middle central panel:
he is lying on the ground, his head is tilted, his pupils are white while his eyes are left open, his tongue came out since the muscles got loose, and there is an eerie? sfx. This happens right after he says his thanks and finally gaining some peace, thus him being dead is almost certain.
The grandfather situation actually mirrors real dogs (in our world), that are capable of extending their lifespans with sheer will power, for their masters. In those cases, the dog usually dies right after it's master (they do it so that their master won't be alone at his/her deathbed), or they simply loose their will to life. In this case, the old dog sustained his life through his rancor/hatred. It's possible that Komamura himself will find another way (basing on his character) and indifference to his grandfather that survived on hatred, he might survive depending on his own duty and loyalty to his mission and people that he swore to protect... it depends on what Kubo wants to do.