Where's the illusion? If the players know that they are going to be confronted by (say) Orcus cultists whether they choose the right or left path, then the choice of path is mere colour.
In fact I don't think the scenario you've described has ever come up in my 4e game - as best I can recall I've run two dungeons of any meaningful scale in the campaign, both at heroic tier. One combined elements of Night's Dark Terror, Sceptre Tower of Spellgard, and maybe some other stuff that I either made up or found somewhere else. The other was the Well of Demons from module P2.
The former had a map and key in traditional dungeon style, and was not strictly linear, but certainly had a general trajectory to it. It's now over five years ago, so memory has faded, but there was undead/Orcus-y stuff pretty much everywhere the PCs went.
In the absence of divination spells or rumours of the classic D&D variety, the sequence in this sort of dungeon has little narrative/play integrity: when the players are choosing to go down corridor X rather than Y, they are generally not making a meaningful choice. The reason for respecting the pre-mapping and stocking of rooms is to preserve the integrity of the backstory that it represents (and for all I can remember, I may have made changes along the way to strengthen that backstory prior to its revelation).
The latter had two phases that were basically linear (an entry chamber, then a big encounter with gnolls and a demon, that I handled a bit differently from how it is written), then three or four McGuffin-collection phases that are basically arbitrary in their sequence, then a big finish.
This is more than four years ago, so also somewhat faded from my memory, but I remember that this is where the drow PC acquired the demonskins to make his robes as part of the process of becoming a Demonskin Adept. But the big finish was the main thing, and it involved rescuing villagers who had been sold to the gnolls by duergar slavers, and were to be used as sacrificial victims. I remember that the players were very cautious, their PCs lingering in the doorway and taking it slow while the gnoll leader tried to complete his ritual - and as a result one of the villagers was killed.
That was the real decision point, and not illusionistic at all: the PCs could have rescued both the prisoners had they chosen differently (and been successful on their dice rolls).
Most of the travel in my game that is not just handwaved is handled via skill challenges (through the wilderness, at heroic tier; through the underdark, for the second half of paragon tier and again at epic in pursuit of Torog; through the Abyss in early epic tier). In the skill challenges, turning left or right is not to the fore - the decision points are framed via the skill challenge, and are resolved non-illusionistically.
Not too far upthread I described a recent episode of play (and have written a fuller account on another thread). Why did the PCs find themselves fighting Lolth? Because they travelled through a portal to the Abyss with that express objective - one of the PCs was built by his player to be an anti-Lolth crusading drow. The scene-setting was not illusionistic: everyone at the table knows why (at a meta-level) I happened to have the dwarf who missed his attempt to leap onto Ygorl fall down to a githzerai earthmote with an Abyssal portal on it.
