What is the Shar'i (Islamic legal) position regarding not reconciling with a deceased maternal uncle after a dispute?

You should have taken the initiative to reconnect with your uncle. However, if you have firmly resolved to reconnect with your uncle and end the dispute with him after your return, and you have taken all possible measures, then you are not severing ties of kinship. Indeed, a firm resolve coupled with doing what is possible is considered equivalent to the act itself, and you will be rewarded for it, as explained by Sheikh al-Islam Ibn Taymiyyah and Ibn al-Qayyim. If injustice resulted from the dispute, then you must repent to Allah and feel remorse, in addition to absolving yourself of material injustices and returning your uncle's rights to his heirs.