If you get the G42 and sell the G26, then you will end up buying another G26 sometime down the road. The G26 is the kind of gun you always go back to if you remain a Glock fan. They are just too handy and take the greatest variety of mags out there(I love that G18 33 round mag!)
Agree. If you can keep both, do it. I have a G19 that I consider my main carry weapon. But I do carry my G43 quite a bit depending on where i'll be going, what I'll be doing, attire, etc.
Biggest advantage of the G42 that I see is that it's small enough and light enough to slip into your pocket. But There may be days/nights when you wish you had that double stack G26 to carry.