>would resistance also potentially cripple the cancer cells?<

this is the concept of genetic baggage, and metabolic budget.

there is only so much energy to a cell, and scant amounts to "waste" on preservation of something that is not used. in the long term, carrying unused properties are disadvantageous, and reduce reproductive output [replication]

the result is "unfettered" oncocytes outgrow those with baggage, and occlude access to resource. if there is no challange that reduces population of nonresistant cells, the resistance will be minimized and extinct in the face of large disparity of success.