I do think that Borlock's death jarred something in Delvin and probably that would not have happened otherwise. Him trying to understand his friend's death was most likely his psyche coming to terms with what possibly lay ahead.
Real courage is when you know you are licked before you begin, but you begin anyway and see it through no matter what! (To kill a Mockingbird - Atticus Finch) Harper Lee.
I believe Delvin is deeply mourning the loss of Borlock, who was not only his friend but also his mentor. Borlock's passing has made Delvin realize the profound impact he had on his life. Had it not been for Borlock's demise, Delvin might not have comprehended the true significance of his teacher's role. Indeed, it is through Borlock's death that Delvin inherited the stone, setting in motion the captivating tale of his adventures. The loss of his dear friend has become the catalyst for a transformative journey, shaping Delvin's destiny in unexpected ways.
I think it's pretty normal for Delvin to contemplate about Borlock's death. Given that how strangely it happened and how Delvin couldn't understand what Borlock was asking him to protect. And not to mention that how great of a friend and mentor Borlock was to Delvin.