Yes, a car with air suspension can be converted to a strut type suspension using a conversion kit. Conversion kits can replace a vehicle's air suspension system with a non-air or non-electric suspension system, removing electronic adjustable shocks and struts in favor of conventional components. Some say that a coil spring conversion can reduce the risk of airbag failure and restore a vehicle's ride height. However, others say that a spring conversion is not as high quality as air ride, and that the ABS/ESP may be offline, which is a safety issue.
Some companies that offer conversion kits include:
Arnott Industries
Offers coil spring conversion kits, also known as delete kits, for older vehicles or vehicles with many air system issues
LEACREE
Offers an air spring to coil spring struts conversion kit that can restore a vehicle's ride height and reduce the risk of airbag failure
Monroe Shocks & Struts
Offers suspension conversion kits that can convert a vehicle's factory-equipped air, hydraulic self-leveling, or electronic suspension to a conventional suspension