With the new PS5/XBox X having just launch and the Switch still doing very well regardless, I was wondering. Lack of power seems to affect the system very little in regards to sales, as well as availability of most major 3rd party multiplats, the console is selling regardless of those. Considering how the Switch has fully occupied the handheld market and it's probably going to go toe to toe with the 9th gen consoles, will the Switch do well enough for long enough for Nintendo to consider  keeping it alive until the launch of 10th gen hardware? What would need to happen for it to last that long?

If the PS6 and Xbox 5 arrive in November 2025, perhaps. That is still a while for Nintendo to wait.
If Sony and Microsoft wait until November 2027, no. The Game Boy (it doesn't matter whether or not you consider the Game Boy Color a mid-gen refresh or successor) is the only piece of successful gaming hardware in history I can think of that went a long time without a successor. I understand Switch is in some ways in its own lane like the Game Boy, but I don't think it would be the best idea. New hardware can excite consumers. And there can be new features in a successor that go beyond better tech specs.
I think a Switch successor should come out in 2023 or 2024. If they wait until 2025 or beyond, they really need to launch a Switch Pro or Plus in 2021 or 2022.
They also need even more compelling software than they already have if they are going to wait until 2025 or beyond.
-Mario Kart 9
-Super Mario Odyssey 2
-Pokemon Gen IX
-Nintendogs

Well they can follow their own path and decide when the gen starts, can't they ?

And today is the launch of Hitman III, the first official game to launch on the PS5 and Series X as well as the Switch on the same day. I think Nintendo will adapt until maybe 2024-2025 and then decides to launch a new console.

And I think Nintendo won't launch a new console before somebody (let's say NVidia) produce a chip which would be nearly as powerful than the Series S (and the Apple M1 showed that in 5 years we can match that in a mobile chip)

There is a saturation point in the market where everybody who is interested on Switch would have bought one already

And I'm sure this saturation point will come way before 2028 (when 10th gen is probably launching)

The only scenario I can see this happening is if both PS5 and XSX bomb so hard that both Sony and MS will hush their next hardware like Nintenfo did with Wii U

When you say "keep the Switch going" I'm guessing you're referring to systems being manufactured till about 2027. I say 2027 because it seems Sony and Microsoft are OK with 7 year console life cycles. However that could change this generation with 5-6 years since technology is progressing fast. I think it can last till 2027, but the games need to keep coming and the system's need to have good prices. Imagine in 2024 the Switch Lite is $100 and the regular Switch is $150 along with Nintendo Selects for $20 each. They need to pretty much do the same thing they did with the 3DS. The 3DS lasted until late 2020, so about a 9.5 year life cycle. Think about that, this very weak system came out at the end of the 7th generation (and kickstarted the 8th) which was nearly 3 years before the Xbox One and PS4 released, and ended production just 2 months before the Xbox Series and PS5 released. On top of that it had no new major games for over a year from 3rd parties and Nintendo. That system kept going for another year because it was very cheap and the games (Nintendo Selects) were cheap also. Since the 3DS could do that then I think the Switch can also. The 3DS's life cycle was 9.5 years, so if the Switch can do 10 years then it would still be around in 2027, which is when the next Xbox and PS6 are predicted to release.

No. They can sell it until then but its momentum will be long gone by then. You can only get so far until the market is saturated.

I don't think Switch 2 can launch the same year as PS6, but I can see a scenario where Switch 2 launches 1-2 years before PS6.  That would clearly put those systems in the same generation whereas now the Switch launched 3.5 years before the PS5, so people are unclear how to classify it.  So if Switch 2 launches in 2025 and PS6 launches in 2026-2027, then the time frames of the two systems would be closer in synch.  But I don't think Switch 2 will launch in 2027, for example.  That seems far too late for a possible launch to me.

Only if they come up with a Switch pro thats alot more powerful.

Hmm no i don't think the next gen will come before 2026-2027. I do think they will launch the successor around the time we will see a mid gen upgrade for the PS5/XS