@Christina Scott good question — this comes up a lot with high-rate GNSS setups.
The short answer is it doesn't really "step down" gracefully in the way you might hope. What typically happens with partially obstructed signal is the receiver keeps trying to maintain the fix at the configured rate, but position accuracy degrades before you actually lose fix entirely — so you'll see increased position error and higher DOP values before the fix drops out. Near a window with decent sky view you'll usually hold a fix, just with noisier output than open sky.
The indoor-to-outdoor transition is where it gets interesting. Re-acquisition time depends on how long you were fully blocked, but with a module like this one at 18Hz, once you're back in the open it locks back pretty quickly — the high fix rate actually helps here because it's continuously updating its almanac/ephemeris position estimate so it doesn't have to start from scratch.
For a hybrid setup the practical advice is don't rely on raw fix/no-fix as your state indicator — watch your accuracy estimate or HDOP value and use that to decide when to trust the GNSS data versus fall back to whatever other sensor input you're fusing it with. If you're doing any kind of Kalman filtering or sensor fusion, that transition zone becomes way more manageable.
