There are excellent GPS based AHRS units commonly used in GA that would give the required information to keep control of the aircraft while they regain situation awareness and sort out any technical issues. These units only require a power source and have a back-up battery and provide GPS ground speed (that can be switched to IAS...but why would you?), GPS track, GPS attitude, GPS bank angle and GPS vertical speed. Certainly more use than a liquid compass with a correction card or a standby horizon that requires data from faulty aircraft sensors...cost...£1500 to £2000.