I don't deny that this might be a logical perspective on the condition that you accept the postulates of Islam. The postulates themselves, however, are simply stated and affirmed, and I see no sufficient reason for believing in them.
Let me ask you another question: what is, according to Islam, the after-life destiny of a morally irreproachable and devout Christian?
Your question is based on the belief that all religons offer the same idea, the roads to it may differ but the destination remains the same.
I'm greatly opposing this belief and i think if a religon is to claim itself true it shall pass the simple criteria of reasoning and evidence, if a religion is truely true then other religons shall stand no chance infront of it.
Now if you have watched the 8mins clip i recommended earlier you shall know what i exactly mean by logic and evidence in regard to religon, if you haven't yet, then i recommend you to watch it.
Mostly atheists and agnostics and alot of religons consider themselves as supporter of the religon of humanity, that we shouldn't say that one religon is better than another, in doing so, we are totally ignoring an important aspect of human understanding, which is reasoning.
We are ignoring the fact that people in diffrent percentages whether they accept an idea or not; their idea can be wrong the same way we all once believed that earth was flat and it turned to be wrong.
Our opinions of the religons discussions doesn't count infront of those who dedicated their lifes in the religion comparison field, if we want to know more about the true religon, we shall be looking for something flawless, something which doesn't have mistakes that contradicts with the basic human logic as well.
We shall look for the results of the debates that happen between scholars that represent us and represent other religons as well, in doing so, we are adding atleast the element of Reasoning if not Accepting.
I do believe Christians will go to heaven if they truely follow the teachings of jesus, the jesus we muslims consider to be true and praise which requires to look at jesus from another dimension, if not, then i believe they will go to hell.