This isn't gonna happen as S1mple will likely leave for another team (Likely FaZe) after the major. In fact following the timeline, its even very likely that Zeus knowing S1mple is probably leaving the team in early 2019, is one of the factors that influenced Zeus into realising that after that is probably the best time to hang it up. He's already confirmed himself that its very likely S1mple leaves to another huge org as there are a handful interested in him, and considering how vocal he was about their fight to keep S1mple in NaVi during the whole Immortals ordeal, I think he recognises how vital S1mple is to the squad's performance and how much harder it'll be when he leaves.
Now in a very unlikely but alternate scenario where NaVi somehow [persuade S1mple to stay with them, then its likely Zeus will be content to play longer with the team and IGL, or if he does still retire, then I can easily see S1mple fully taking on the IGL role for NaVi, and it might not be as bad as people think. I think while it will put more pressure on S1mple's plate, which there is already a fuckton, it will benefit the team performance overall in the long term provided Zeus is replaced with a solid fragger and the team's potential will definitely be raised much higher if Edward is replaced with a proper support role player who has a good sense for the game at the elite level, and actual good utility usage. S1mple already has a lot of input in NaVi's play and is much more driven than anyone in CS right now, plus he has a good big picture read on the game which is beyond obvious when watching him play, as well as the foresight on how to improve a squad with time (he was the person who pushed for the Electronic signing and integrating him better into the team, which has been very impactful for NaVi).
Those are the reasons why I can see S1mple as a very good IGL for NaVi in this alternate scenario,. However while it may benefit a Zeus-less NaVi, its far from an ideal scenario for him as an individual. Best case scenario for him is to move on to the next level of his career, sign with an international team with much higher skilled teammates on average, where he can properly take it to Astralis and maybe consistently win tournaments, while improving even further as a player.