It seems from other crisises, Installing to 4.3 would indeed delete you hombrew, and it would be near impossible to get back.
The reason is because we've, i believe, hacked our way through 4.2, but the "changelog" of the 4.3 effectively states:
Changes
Deletes the Homebrew Channel and DVDX, title IDs HAXX, DVDX, JODI, DISC, and DISK.
Now uses IOS80.
IOS254 stubbed BootMii is deleted.
Fixed Bannerbomb less stupidly this time.
Added IOS58.
HackMii Installer Userland+Syscall IOS exploit removed
NANDFS privilege escalation fixed
ES_AddTitleFinish now checks the signature (Trucha Bug Restorer and similar won't work anymore)
We beat 4.2, but nintendo did it right this time