Another useful item in a glass cockpit when pressure-driven instruments are offline is the Flight Path Vector - if one's fitted, of course!
If you want to fly S&L, which is a good idea while you sort out what's working and what isn't, just manoeuvre the 'bird' onto the horizon: that stops you going up or down. You can then set a datum power from your 'flight with unreliable airspeed' tables.
If you keep the gap between the pitch bar and the FPV constant (c. 2-3degs in the 777, probably not too different in other jets), then you'll be somewhere in the middle of the speed range for your configuration == safe. If you notice the gap reducing, you're getting faster and vice-versa. It's a good cross-check against other sources of information - effectively you're flying AoA and should be able to approach and land without reference to any other instrument...