There is no I2C driver, you have to write your own.
That said, as written in the following page :
LoRa Basics™ MAC is scheduled to be deprecated within the year.
Semtech recommends that people designing new LoRa®-based solutions use LoRaMAC-Node instead.
In the past weeks I have had continuous contact with Semtech and was involved in the TAP program for this stack (last contact was just a few days ago!). The focus was heavily on improvement and not once it was mentioned that it could become deprecated. So this is kind of out of nowhere for me and my team. We have invested time and effort on this from our side, so I would like to know why.