If Stirling was killed by the Aborigines then the settlement of Perth was already underway. I don't think that his death would have stopped that. Stirling was more belligerent toward the Aborigines so his death possibly lessened tensions but I doubt it.
The settlement wasnt underway at that stage. Maybe I wasnt clear on when..Stirling explored the Swan river and its upper reaches in 1827 and met with (angry) aboriginals then. He eventually got back to London in 1828 and lobbied for a settlement, which as we know was founded in 1829.
If Stirling was to have met his demise in 1827, I think that the dutch may have come across it (again) on the way to the East Indies and settled it a bit quicker as Govenor Darling probably doesn't want to send anymore resources as his own colony in Sydney is having its own problems.
The Dutch would certainly have come across Lockyers settlement at King George Sound eventually or vice-versa. Interesting times...