There is already a temporary fix for this issue, which can be found at: MCL-5291

The temporary fix doesn't work for long, as the Native launcher updater decides to again run the 39.85MB and again gives me the error code 5. What I have found that fixes the error code 5 message for me is the following:

If you renamed that .tmp file to Minecraft.exe and left it in the tmp folder, just recopy that minecraft.exe file back over into the NEW Minecraft folder you create from the instructions given in the temporary fix, and this for me, gets me past the Native launcher updater. This temporary fix only works for so long however and then the Native launcher updater decides to run again, giving the error code 5.

Mojang, can't you just reinstate the original launcher that did work, until you iron out all the bugs with this new launcher? Or is there a way to turn off that damned Native launcher updater?