One would probably engineer these cells with a killswitch, such as doxycycline induced Caspase9 https://pmc.ncbi.nlm.nih.gov/articles/PMC1895037/.

The transgene engineering is totally possible without a viral vector. We engineer cells all the time with recombinase based editing methods for targeted safe harbor insertion of transgenes https://www.nature.com/articles/s41551-024-01227-1. This stuff just permeates through the community slowly.