The MG43 simply would not exist as it was not developed until the late 90's.
It's worth noting that a number of support weapons, including the RPK series, do not have changeable barrels. Therefore, it's
possible the LMG11
http://guns.wikia.com/wiki/H%26K_LMG11 would have seen production. With it's 300 round internal magazine, and
light support role (i.e. not intended for sustained fire), the lack of a belt feed is in my view (as an ex machinegunner) is a plus, not a negative.
Belts are a pain in the rear when moving about the battlefield. A 300 round belt of 7.62 is about 3 metres long, 5.56 about 2 metres give or take. Yes there are various "magazines" to hold belts, but these are still limited in size (the FN Minimi for example has one of the largest at 200 rounds).
Personally, I'd much rather change a mag every five minutes than haul a belt around.
However, in a defensive position or mounted on a vehicle where the ammunition doesn't need to be hauled around, a belt fed weapon is hands down superior.