An update would probably only download and replace the parts of the Wii U's software that that particular update was meant to "fix"
If the update was just meant to make the Wii U mode load faster or add better USB support it would not need to do any changes to vWii for that and so would probably leave it alone .. and it would stay bricked in that case.
On the other hand, if one of the things it wanted to change WAS vWii, then it would be downloading new parts of the vWii and installing them.
IF one of those parts being installed was one of the ones that caused the brick, it very well may fix it.
The thing is, though, there's really only 2 reasons I can see them wanting to include a vWii update.
1. Some of the Wii games out there just don't work on vWii. An update might be made to fix that.
2. They might also just update the vWii to try to block Homebrew in one way or another.
The first one could be done in two ways.
- If it's a problem that they need to make a fix in the IOS that the particular games uses and that's all they replace, a brick is more likely caused by a problem in the IOS used by the system menu or in the system menu itself ... and that would NOT need to be replaced in that case.
- If it's a problem that they can have the system menu patch when it's loading the game (kinda like how ocarina cheats make patches, for example) THEN they would be replacing at least the system menu itself (although maybe NOT replacing it's IOS) so it that's where the problem lay with the brick, then yes, it could fix it.
On the other hand, if they're trying to block homebrew, there's ALL KINDS of stuff they could try replacing. Again, IF what's broken get's replaced, it might fix the brick. (You just wouldn't be able to enjoy your homebrew anymore)
There's also the possibility of them updating in such a way that it would simply screw over anyone who had homebrew already and CAUSE a brick for them and leave "legit" users alone. In that case, it would stay just as bricked as before.