A: Before answering this question, we should also try to ponder on other questions similar to this:
When a Christian steals a pen, is he still saved?
When a Christian curses once within the whole year, is he still saved?
When a Christian flatters someone as a form of lie, is he still saved?
When a Christian thinks negatively of the people around him, is he still saved?
Just because people think that the sin committed by a Christian is that "big" (like suicide), it doesn't mean that he has lost his salvation. I mean, a sin is still a sin, right? If there's such a thing as "losing salvation" then nobody will really be saved...
If people believe that they can lose their salvation, then how will they be able to get it back? By crucifying Jesus Christ on the cross again? I don't think so...
As Jesus said on the cross, "It is FINISHED". As Christians, we still fail God daily, and the only thing we can be proud of is His love for us. In church, even if Ephesians 2:8-9 is mentioned over and over again, some of us still miss the GRACE part..
But then again, this doesn't mean that this gives us a license to sin. On the other hand, what difference does it make when a Christian commits suicide? How different is it from other people's flaws, or better yet, sins?