Is it okay to leave testicular torsion untreated?

Yes: Untreated testicular torsion can result in the loss of the testicle. Additionally, the oth testis is also prone to torsion, and is at risk as well unless fixed in position ( a procedure called orchidopexy). Even if the pain symptoms go away, you need to be promptly evaluated by an urologist.

Yes, at times....: If a typical testicular torsion has been around more 8-12 hours or days with no concern for infertility and protracted timing for recovery, leaving it untreated may be justified and reasonable if patient wishes and agrees to. But after all, surgery is still best and surest for shorter recovery and future.