Mantis was dealing with Nathan Petrelli at present, a man whose stubbornness was near legendary in the circle of those who knew him and even that forceful gaze didn't derail Nathan from the opinion he had formed, the look he returned one that was unflinching. They all had pasts, some much worse than others – and in some cases, futures yet to happen – but Nathan only counted what was here and now for many of them, because that was what he tried to do most days, live in the now. To dwell on the past (or assume the future would come true) was to tear oneself down and he had done that to himself, but he had also pulled himself from that eventually to look back on his life, face the truth of what he had done wrong and then fix it.
Despite this, he didn't argue it outright. He sensed it would be pointless, given that he was certain Mantis sensed his opinion hadn't wavered and the only person who could truly change Mantis' mind was Mantis. It was enough for Nathan that Mantis knew how he felt.
However, the claim Mantis would not always be around momentarily threw Nathan and then made indignation rise from the place that silent worry always was. They were at the mercy of these Powers That Be, or whoever else was involved, and at any time they could be plucked from this time and sent home. He tried not to think about it usually, because it was unacceptable to him that it could happen and he had no solution to it yet. He wouldn't leave behind all those he cared about who weren't from his own world and he damned sure wouldn't leave Peter here, or worse, have his brother return to that living hell of a future.
But it was a valid question. For however much he wanted to rail against the entire process, he still needed to be realistic about this because it concerned Peter. If Mantis was gone before Nathan discovered an answer to this dilemma, who would be there for Peter as Mantis had been?
He gave the suggestion the weight it deserved before answering. "I know Peter would do well with him, but do you think Luke can handle him the way you've had to in the past?" he asked, dropping his hand from Mantis' arm to run it through his hair. "I don't want Luke hurt, and Peter wouldn't want that either."
Though he had been saving the question for last, it now seemed to fit, likely due to the fact they were discussing Luke.
"And you mentioned the Dark Man, when you asked about Peter," he said, studying Mantis. "Is he still a problem?" Nathan, of course, had no way of knowing that Exar Kun's latest exchange with Peter, as well as his mother, had been filtered from his computer by Peter.