I'll try to answer from just a slightly more general perspective, mainly exploring the issues outside of the mere sale for gaining gold, keeping in mind that you don't seem to care much about the fate of the character, rather than that of their items.
It entirely depends on you and your players
If they think they are being robbed of part of their progress as a party, since a character and all their findings are de facto disappearing, I feel they should have the right to claim some of that character's worth. Since the Wizard was a member of the party, his items were obtained with the contribution of everyone (more or less). One might argue that the other characters just gained something out of nothing, but this "nothing" is itself arguable, as I explained. Talk with your players about this: do they just want a boost in gold or do they feel deprived of their achievements? A sudden increase in gold might be a problem anyway, so you might want to balance that in some way or just prevent the PCs from getting their hands on the items.
Justifying the gain (or loss) of the items
It doesn't really matter if the players do not care at all about roleplaying in this context, but assuming they do, it might be quite awkward to simply have the items appear in the others' inventories, or have them lost due to the PCs vanishing from the world, as in a previous campaign of mine (mentioned later). You might want to spend just a few lines to simply mention what was of the character, without digging into details. You can have the Wizard killed in a tough "off-screen" fight, which is independent from the PC's background. Mourned by his fellow adventurers, his body is buried during a ceremony filled with grief, together with anything he held dear. The rest is kept by his friends (otherwise, everything is left in the tomb). If it fits the character, he leaves the items behind for his friends to continue their epic quest (otherwise, he keeps everything with him), while he retires to lead a life of study, or travel on a spiritual journey, or start a drug-trafficking business in a van with one of his students. In the end, whatever fits your story and doesn't feel awkwardly forced to anyone.
In the past, I had two players suddenly leave for personal reasons. No one complained about the loss of their inventory, mainly because there was no real reason for their PCs to leave and we felt that having them killed or whatever just to get our hands on their bags wasn't right. We also didn't really care about the roleplaying of such an event, so we outright had them "disappear" as if they had never been there in the first place and our characters would have no memories of them at all.
Gameplay-wise, however, those items may break the balance. You will have to deal with that, if you choose to handle them over.
Balance might be an issue
Fewer party members with more magic items (or whatever) might throw off the balance of the game. Speak with the players about this concern (if it really is). You might rule that the gone PC was the only one with the knowledge required to wield those items, others have to study/train in order to do so. Maybe one item is peremptorily out of the others' reach, as only a high level Wizard is competent enough for that, but they can still sell it. If you are concerned about the amount of gold they might make from the sale, aside from preventing the PCs from laying their hands on the items, you can make it more difficult to find somebody who would buy them, or even more, who would buy them at the just price. Maybe the other PCs have no idea of their real value. Perhaps they have no trouble gaining a fair amount of gold from the sale, but after that they won't find anything valuable for a long time.