How Long is Too Long to be Gone while on maternity leave?

Hi, I'm currently working with an agency and deliberating their maternity leave conditions. Has anyone who has talked about maternity or paternity leave with current (or previous) employers found the decision was being constantly deliberated? The pros and cons have been weighed for me to stay with the agency but with contracts was there an agreement you had to draft then redrafted? Have any you found you've changed your minds mid-leave or is there preassure to return? Would a career change be better? If you have to start again do you worry about experience or do you only apply for jobs you know you have experience with?

Thanks for any help you can give me