The current motion is against the PM, not Government. Personally, it's I think it's political posturing which won't lead to anything because the Tories will not want to look divided to the public and the implication of this motion winning is a process that leads to changing the PM. Hence, the Conservatives are rallying around their leader.
This picture becomes far more complicated if the Government loses a parliamentary vote on May's deal. This is because the country will be headed toward a no deal Brexit which MPs are opposed to. Despite people like Rees-Mogg saying they'll support the PM in this motion, it doesn't change that people like him will still vote against her deal. To quote Rees-Mogg from The Brexit Lectures (BBC iPlayer, 23rd June 2018) he said it's even worse to be 'vassal state' than a full member of the EU. I doubt that this fundamental schism can be mended, and if JRM actually backs this deal, it will be a monumental sell-out. In fact, I'd argue that May's deal isn't a real Brexit and frankly, Barry Gardiner lays it out better than I could in the linked article where he says it'd 'con' to the 52%.
If faced by a real prospect of a no deal, then it's conceivable pro-Remain Tory MPs would back a motion of no confidence in the Government.
Brexit means leaving the single market and the customs union. Here’s why | Barry Gardiner