Well we'd obviously have about a decent amount of cap space if Parker retired and Glenn & Wallace were moved on, some of which would go to re-signing Gillett, the rest can go to signing depth forwards.
I don't really see how our strong forward pack turns into "severely understrength", could you please enlighten me on that? The only significant loss would be Parker, who does all the dirty work in attack and defence. Arrow has all the makings of being an extremely similar player long term, literally averaging like 220 metres and 45 tackles game in the ISC. We'd also probably gain some grunt by replacing Glenn with Thaiday (This really would only work if Sam was motivated to lose a bunch of weight and finish his career in the second row)
The rest of the starting pack remains the same, and our bench arguably gets stronger, with another season of Ofahengaue getting better, and Ese'ese & Pangai just being enormous skillful humans that would provide far more impact than our current bench does.