The 430W will not switch from VOR to GPS automatically. However, it may automatically switch from GPS to LOC. First, there is an internal menu setting to turn this function on or off. Second, you must have loaded the ILS into the 430. Finally, there is some criteria that must be met - something like at least 2 miles outside the FAF, so if you get vectored in too close it won't switch. Frankly because of all the variables I recommend pilots get in the habit of switching manually. OTOH....
I have a 420W and an SL30 feeding a GRT HX EFIS. If I arm the ILS approach on the HX, then it searches all the nav inputs looking for a localizer frequency, and, at intercept, automatically switches from GPS (or heading hold, if in that mode) to the localizer signal.
Plus/minus between a 430W plus #2 com, or a 420W and an SL30:
Sl30 is a superior vor, actually two VORs or one vor/one ILS in one box.
SL30/420 doesn't put all your eggs in one box
430W/second com is about $1K cheaper.