Good god no.
The iPhone was out two years ago before the N900.
Nokia was already fucked because it had set up a system in which internal divisions designed competing phones, as a result it had flooded the market with similar but-not-quite-the-same handsets with overlapping features, and it had missed out on usability advances that iOS had made.
Symbian was undergoing an overhaul which would eventually lead it to be ’good’ again, but by then it was too late as Android and iOS were already eating its lunch. And around the time of the N9 launch (touchscreen-only Maemo/meego phone), Stephen Elop took the helm and issued the famous “burning platforms” memo which put Nokia on the path to windows phone exclusivity, purely to the benefit of Microsoft, who delivered the killing blow by first forcing the doomed “Windows Phone” onto them, then buying the mobile phone division so MS could churn out more doomed handsets for their stillborn mobile platform.
tl;dr - The company was a clusterfuck riding on name recognition and then an MS plant killed it.
Linux on the N900 was neither here nor there. It was a skunkwork effectively, a niche device for nerds (and a great one). But it neither sank the company nor could have saved it.