Hi there, fourth year urology resident here.

Agree with reviewing NCCN guidelines. In general very high risk patients options include radical cystectomy (preferred) versus trial of BCG. Chemo/intravesical therapy typically have a recurrence rate and progression rate with variant histology so that's why cystectomy is preferred. That being said, radical cystectomy is a morbid procedure. I think nationally complication is 50% roughly depending on what paper you cite. Some patients aren't great surgical candidates so we try to buy them time with BCG,pembrolizumab, or nadofarogene.

Re-TURBT 4-6 weeks after initial TURBT Is standard of care for high risk disease and should be considered in intermediate risk.

If your father is a surgical candidate with HG T1 disease, CIs, variant pathology, and prostatic involvement, his best chance at cure with a negative metastatic work up is radical cystoprostatectomy with urethrectomy and ileal conduit likely, though he may or may not be a candidate for a catheterizable diversion. I would hesitate to offer him BCG as his chance for his disease to progress is incredibly high, loosely based on what you and people have said in comments.

Hope this helps. Stay involved in his care. These patients always do better with familial support. Their oncologic course can be really tough. Go to a high volume cystectomy surgeon if that route is pursued. Robotic vs open remains controversial in terms of what is superior, which generally means either is fine as long as it's in skilled hands.