Does not proceeding with the matter negate the content of the Istikhara, knowing that the supplicant felt a sense of relief and certainty towards it?

If you have sought Allah's guidance through Istikhara concerning a matter, but were unable to pursue it due to unavoidable circumstances, then this is the best outcome, because Allah did not facilitate it for you. Istikhara does not depend merely on a feeling of comfort or discomfort in one's heart. Rather, the one performing Istikhara does what they deem appropriate, and if the means for it are facilitated, then that is what is good for them. There is no mention in the hadith that Allah instills a feeling of comfort in the heart of the one performing Istikhara, or that they see a vision, or hear a voice. In fact, one might not find any comfort in their heart even after repeatedly performing Istikhara.