I usually perceive these ultimatums as PR stunts to the general public, so as to not appear too strict, or to appear merciful, reasonable etc. I don't expect people to actually turn themselves over.

I wonder if Iran is simply lying (adding an extra headache to mossad: figuring out if their agents are compromised) or if the collaborators realized Iran's intelligence services are good enough to catch them. And of course some may have regretted their involvement.