I think they will get some follow up. After AE, Perturabo is still left out there on his own to brood / rage etc. In my eyes he has a way to go before he falls. He still has the siege engines for terra.
Unlike many others, I liked the portrayal of Perturabo in both phall and AE. AE went into his psyche in depth and in Phall, it was more of a snap shot of a him as a primarch at war (stern, unforgiving). I also loved the iron warriors in AE. I had not read the 40k iron warriors books, so there was no complaints about re-use of characters from me.