[Skidz]

Igor, tail strikes generally don't take out servos. If they are belt drive type, they can take some teeth off the main gear and the belt drive gear coming off the main gear.

You tend to lose a servo when the main blades strike the ground. You lose your main blades too as they don't generally survive. Forces get pushed through the links from the swash to the servo arm. The small plastic gears under the cover loose teeth. When it first happened to me, the servos looked fine but I noticed I had a hard time hovering and it frequently shot up/left and was a real handful. It was missing teeth allowing the swash to slip without command.

HXT900 servos are so cheap you wouldn't repair them even though you can. Try them by all means but get 6 at least - possibly 8.

If you ever upgrade to flybarless in future, get the Align metal gear ones on the link I gave you above or equivalent units, and replace them on your heli. Flybarless set ups have links that literally go from the main blade to the servo arm putting a lot of force on the servos mechanically. Flybarred helis have extra links that reduce the forces at the servo so not quite as tough on servos as flybarless.