Uh, no. Sentient beings are not merely physical components. A sentient entity is a system -- especially a mind, which is a complex system of neural interactions. When that system is dismantled and its components used to create a new system, that person is therefore dead. You might as well argue that George Washington isn't really dead just because the particles that made up his body were later absorbed by other organisms.
Besides, Tuvix clearly did not have the actual physical mass of two men; ergo, a significant amount of physical matter was lost in his creation.
Leaving aside the philosophical considerations of the transporters mechanics and abilities, the fact is that Tuvix did not
have the mass of two men, but then, neither did Neelix or Tuvok have half
the mass of Tuvix afterwards. Therefore, mass in the transporter is apparently not a strictly physical quantity but more of an informational state - the information of Tuvok and Neelix was superposed as Tuvix, and the Doctor merely separated the information of the two. I can't explain how it works, because 1) it's far more advanced than our 21st century technology, and 2) it works according to the principles of plot requirements.
My question is, what was lost when Tuvok and Neelix were combined, and what was gained or lost when Tuvix was deconstructed into his components? If the memories of all three were retained before and after, the knowledge and skills were retained before and after, then what was gained or lost in deconstructing Tuvix?