Turbo siezed

Yes and yes. But I'd say a hose dropping off and stopping it making any boost is more likely.

I sort of meant, if the turbo siezed solid due to lack of oil would the resistance to the exhaust be so great that the car would be undriveable. ?

No. It will be noticably underpowered, but probably not actually undrivable.

Nah, not really. It should be OK, just won't pull nearly as well.

It varies. Sometimes they'll still be driveable, but exhibit a total lack of power, but others, they'll struggle to even start.

How's that work then?

If the turbo seizes, then you're placing a restriction on the inlet system, and on the exhaust system. Some engines will run reasonably well with the restrictions, but others will just strangle themselves. Generally it's the smaller engines that won't go.

But generally, turbos very rarely just seize. The bearings usually collapse, leading to the turbine wheels hitting the housing and a high pitched sraping/squealing noise, or the oil seals go, leading to the engine oil either being dumped straight back into the engine (can lead to some nice running on) or down the exhaust. Or the shafts snap. Think I've only ever seen one turbo actually seize, but have seen a few with collapsed bearings, and countless more with oil seal failure.

Oh I agree they won't "go" but I've never seen it make any difference to starting.

I'm pleased to say it wasn't seized. I took the air intake off and could spin it with a finger. Annoyingly, even though I am glad it is fixed, I don't know what the problem was. I'm putting more detail in my other loss of power post.

I suppose with a jammed supercharger, it might just.

Though it'd have to be disconnected from the engine by some other fault, so it wouldn't stop it turning over.