Perfect work delivery and in-depth revision and friendly support.
Honestly, Disqus is the best SEO-friendly commenting system out there. Many big web expert company uses Disqus like envato's tutsplus network, laracasts and many more. So, you can understand it is very good.
You will not lose any old comments. I will sync your old comments to disqus. So, your all comments will be fine but appear with disqus style.
Yes, I can fix that. However, as fixing problem takes a lot of time to find the cause of error and to fix it, so you will have to buy additional disqus error fixing gig from me. It will cost a bit but I hope you will be happy after getting the bug fixed.