You pose an interesting question. Short of investigating the German military archives, & assuming that they have complete records for Wilhelm Hoffman (the German government did have a notable problem of keeping its records intact in 1945), we'll have to deal with probabilities.
According to the Wikipedia article on the Battle of Stalingrad, as many as 400,000 German soldiers were involved in the Battle of Stalingrad; the article claims as many as 400,000 soldiers were killed, wounded or captured. Yes, the toll on human life was horrendous. In short, few, if any, managed to escape the encirclement & find their way back to German lines. So any survivors would have been amongst the 91,000 who surrendered 2 February 1943.
These were taken into Soviet POW camps where conditions were equivalent to the notorious Gulag Archipelago. The toll in loss of German life continued; many of the prisoners arrived in poor condition -- sick, wounded, starving -- & the inhospitable environment of the camps doubtlessly hastened their demise. By the time these soldiers were released from their captivity in 1955, only 5,000-6,000 were still alive.
So assuming that Hoffman did exist, the chances that he survived the following weeks until the surrender are slim, worse than 1 in 3. If he managed to survive to one of the Soviet POW camps, chances that he lived to return to Germany are 1 in 18 -- all in all, less than 2% chance of survival. So unless it can be proven he had somehow survived the battle, Hoffman can be presumed to have perished there.
BTW, the question arises: how did this diary survive the destruction of the war to be found & at least partly published? A bit of sleuthing reveals that Vasili Chuikov published a translation of it in his book "The Beginning of the Road" (originally published in 1959, first English translation in 1963), claiming it came from his files. Whether or not Chuikov's book is a reliable source I can't say, but as a Russian general at the Battle of Stalingrad he was in a good position to have obtained this diary, if it is an authentic witness to that battle.