What does "Should we not be able to" mean in the following sentence? does it have a positive meaning or a negative?
Should we not be able to assist you at present, we will be keeping your information on file for future possibilities.
It's a flowery way of saying if. It basically means the same as:
If we cannot assist you now, we will keep your information on file for future possibilities.
Should we not be able to assist you at present, we will be ......
You can use 'should' instead of 'if' to refer to a possible event or situation in the future.
So if you read the clause with "if" as follows, the sentence will come across:
If we are not able to assist you at present, we will be ......
You can also use if and should together to convey this sense as follows:
If we should not be able to assist you at present, we will be ....
However, the use of should in the forms of 'should + subject + verb' and 'if + subject + should + verb' is somewhat formal.