Samsung already does, but they still buy Qualcomm.
If Apple and Qualcomm cannot come to an agreement then Apple should stop using Qualcomm modems. Are they under some legal obligation to use them?
Nope, but anybody building a modem has to pay Qualcomm.
There is no way to do CDMA or LTE without paying Qualcomm.
They invented the technology that makes not only CDMA and LTE possible but some aspects of WiFi also.