How to reply to editor's comment such as 'Such a revised paper may be refereed and there would be no guarantee of acceptance'? Is it necessary?
Is it necessary to reply to editor's comment like this? 


No. This is just making sure that you understand that revising the paper does not guarantee acceptance.

You may wish to write an introductory paragraph for the editor before you address the specific reviewer comments. Here, you may wish to thank the editor for acknowledging that the reviewers consider your results to be useful, summarise the main improvements, and conclude that you feel the manuscript is substantially better for the reviewer suggestions.