Which salvation?
Scripture discusses basically three types of salvation. I am guessing that you are referring to the first type I mention below, but thought it might be interesting to discuss the others as well.
1. Salvation from damnation/separation from God. Also referred to as Hell, Hades, etc...
2. Salvation of the soul also referred to as the "end of your salvation" showing it to be a process that takes place over time. Relative to the transformation of the mind being no longer conformed to this world.
3. Salvation from physical destruction like with Noah, Lot, etc...
The evident answers to these questions would be this:
1. It depends. If one has received the gift of the Holy Spirit, then "no". What God has put together, no man can put asunder. However, if one has only received the baptism of the Jesus' name, then "yes". Jesus said that many would come to Him calling Him Lord and He would say that He does not know them. He said that many would come in His name deceiving many, even the very elect if possible. It perplexes me today as to how many "Christians" are ignorant of the gift of the Holy Spirit just as those mentioned in Acts 8. Did Jesus not say that it was a gift for those that ASKED for it? Why do people debate this? Yes, it is a free gift but it is not given freely to everyone. Only to those that ask for it. Why debate it then, why not just ask for it if one has not yet done so?
2. It is possible to conform to this world, thus it is written that the dog shall return to its own vomit. It is also written that it would be better that some had not known the truth then to do so. I have witnessed this. To be a sinner lost in the world ignorant of the freedom that was given through our Lord Jesus is such a sad thing, but whoa to those that have known the truth and willingly choose to turn back. The way of the transgressor is a hard way but even more so for these. Sin is harder on one that has confessed Jesus as Lord than for the sinner. So yes, one can "lose" their mind (salvation of it) by choosing to conform to this world willingly rejecting the word of God.
3. The last one is an easy "yes" as well. Lot's wife was physically saved but turned back and thus destroyed. If God instructed someone to leave a certain place because sudden destruction was coming to that place (as He has done many times) and one's ear had grown waxed to hearing His instruction and/or refused to leave behind earthly treasures (including people), then certainly they would suffer the coming destruction.
Remember that we are to be comforted in these things though; that God is even able to gather to Himself those that sleep in Jesus. We are not to sorrow over these things like those in the world without hope.