do definately get it fixed. you will run semi limp in open loop for a bit. once the lambdas light off, the puter might be able to use MAF and lambda input to try to trim fuel. but this would be a backwards, deductive means for the puter to trim fuel. just replace it and dont sweat it anymore.
You better believe it. Your computer will be quite confused and you should be running in open loop because the ECU cannot see what temp the coolant is at - so basically the engine should be running rich.
The ECT is a pretty important sensor. The computer will definitely go into a limp mode and it will run decent (but like a rich pig) with it broken or unplugged. Should still be reliable enough to get you around. Only the fuel gauge will drop a lot faster.