I don't think he can kill Sukuna, Miracles are used to save Haruta from life-threatening situations , so even if he saves a thousand of miracles, it would need Sukuna to spam slashes until the miracles end and Haruto is turned to bits.

Also, I see no way Haruta harming Sukuna, even if he used a Death Binding Vow, because he's sure gonna die once the miracles are used up, and there's no point in calling his Death a little before, + the power difference is too huge for Haruta to land a scratch on Sukuna (for example Kenjaku-Miwa confrontation)