In "Timeless" we see that Captain Janeway attempts to land Voyager on a class L planet. What if there was no planet?
Well the ship would have broken apart in space. Would have made it a lot harder to find Seven and the holo emitter.
That there was a planet might suggest there necessarily would be. I mean, odds are astronomically against there being a planet there when the ship hops out of slipstream. And by astronomical, I mean it just plain couldn't happen by coincidence. Never, ever. So supposedly slipstream is attracted to planets. Or perhaps features a prebuilt network of conduits, similar to the Borg constructs, that guides the ship towards specific locations of interest, without our heroes realizing this. And if the ship doesn't understand enough about slipstream to brake hard when exiting, a crash always follows. Not that it would have been a particularly bad crash, mind you. The ship slammed onto a planet after a short deceleration from ludicrous speed and barely got the paint scratched. I doubt things could ever have gone smoother, planet or no planet. Timo Saloniemi
This happens in Star Trek all the time, whether at warp or impulse there's always a convenient planet to crash on.
The only two exceptions to that rule that I recall might be "Disaster" (TNG) and "Where No Man Has Gone Before" (TOS) though the latter is stretching things a bit since they were close to a planet but Kirk mentioned the length of time it would take to get anywhere...
The ship had not a scratch but Troi couldn't land without ripping the saucer apart not at ludicrous speed. How convenient to find the crew. Also not splattered for our family show. Yay!
If there's no planet, eventually they'd run out of power... life support goes down, deflectors go down so meteroids and other particles and radiation bombarding would turn the ship into swiss cheese with BBQ'd crew. The ship would continue in the same direction until it inevitable crashed somewhere, since the meteoroids are too small to have any serious impact - like the gnat flying into the jogger, the jogger isn't going to notice much. It's there, but so minute that it'd have to be a constant steady stream before the ship lost velocity, which would pick up again the moment it got close enough to a planet or star with enough gravity to draw them in. So not just BBQ'd. Fried. Anyone have Teriyaki sauce? Assuming they don't instead crash onto a planet and become jellified? Yum...
Tuvok says they are risking structural collapse if they don't land the ship. This always struck me as odd. If they remain in space, no gravity, no collapse. If they land they have to survive the stress of atmospheric reentry without the benefit of shields or deflectors. Structural collapse would be more likely. I think the best choice would be to float around space for a bit until they get their bearings. They had some thrusters left to guide the ship around asteroids etc.