I'm sorry to hear about the predicament. I don't have any stats and wouldn't know how to search for those because I'm almost positive it would be unethical to conduct a study using people getting sub-standard care.
The trials that have been done look at the number of post-op specimens that have responded to chemo compared to those who have not had any chemo, and found that the people whose bladders show no cancer upon cystectomy/pathology have a better chance of long term survival than those whose bladders still show signs of cancer after cystectomy.
Partial cystectomies are a controversial treatment. Recurrences are so common that most experts question it's usefulness. Once a epithelium of the urinary tract becomes cancerous, recurrence can occur in any part, bladder, ureter, kidney or urethra. The risks remain.
The best bet at long term, recurrence free survival after a dx of muscle invasive bladder cancer is bladder removal, the stats say the sooner the better. Newer stats are implying that pre-op chemo ups those odds.
There is also the bladder sparing option of using the combination of tumor resection followed by chemo and radiation. But the recurrence risk remains, is often superficial and then folks get treatments for that.
Your father's diagnosis of lymph node mets is a scary one, TCC is an aggressive tumor once it gets out of the bladder. It's great that chemo has put that into remission, and it could well happen that your father remains cancer free forever, but it's a gamble, as is everything connected to cancer treatments...I'm sorry and I wish it was different but that's the deal.
The choice is his. Some people are very anti-surgery, the thought of losing a bladder (or any part of themselves) is too horrifying. We all have our limits on what we're willing to go through.
But your father should know that in case of spread, many or most experts would probably no longer be willing to remove the bladder, but will only give chemo and/or radiation. That's because they feel it's not worth the cost and morbidity to the patient because cure is no longer possible, but only controlling it with chemo for as long as that works.
I wish I had more info for you.
All the best,
Wendy