Trump is way out in front now because there are 14 other candidates splitting what's left. The majority of Republicans want someone else. Trump's favorability rating among republicans is still < 40% in most polls. His unfavorability rating is still > 60% in most polls. Trump is at 34% in the polls right now. So still, ~ 1/3 of Republicans want trump. That means 2/3's want someone else. Again this exemplifies the need to knock off this silly two-party electoral system we have and go to a ranked voting system.
As far as Trump running as an Independent, I don't think he'll do that unless he really feels like the Republican party is pulling shenanigans. Running as an independent he'd have to spend a LOT more of his own money. If he lost the primary to someone else fairly, I think he would bow out unless the nominee is someone like Jeb Bush. And that likelihood is very dubious.
