In normal circumstances the coil does not generate a high-voltage spike. It does generate current for a time after the switching device stops conducting.
Volt level will rise according to several factors, including load. With little or no load, the coil produces however high a volt level is necessary to overcome the charge on the capacitor. The output stage can soar to a hazardous level.
In normal circumstances the volt level will not endanger the mosfet/transistor as long as you use one which is rated for your anticipated levels (since the body diode will be rated that high as well). Also as long as you keep a load attached to the output stage.
To see the inner workings of a boost converter, you might look at my video which has animated simulations of switched-coil converters (including buck, boost, and buck-boost).
It portrays current flowing through wires. It shows the flux field building and collapsing. It shows capacitors charging and discharging.
www.youtube.com/watch?v=FT_sLF5Etm4