I understand the first and last words but "can" is a bit confusing as I cannot recall what it means in Latin nor do any of my dictionaries have it listed. Are you sure it was not "an" - as that would make much more sense, or at least I think it would, and come out, roughly, to "None Preserver?" Although if it were "an" it would be a conjunctive and so the statement/question would expect a negative answer. I wish I had more context though, because, while nullus is quite easy to translate, insisto has some other meanings that might drastically alter the sentence. Now remember that I'm a bit rusty so this might not be correct - but that's what I'm getting at the moment.
P.S.
It could be that it was meant as "Can none persevere?" and the "can" was added - but that would be a bit odd.