What are the severe side effects of having a lifetime maintenance of 1/4 tablet of clonazepam (0.5 mg) a day for my panic disorder? pls. answer.

Generally none: This is such a low dose of Clonazepam that it is unlikely to cause any side effects, severe or otherwise. It's also so low that it may not help panic disorder very much either — and there are better treatments for panic disorder than clonazepam. The only real risk is "tolerance": your body may come to expect this medicine, and it will have less benefit over time.