Let say I had a blog post which was indexed by google, and say for some reason I couldn't renew the blog domain for which all the indexed pages and contents are now gone. If I post the same content now in a new blog, will it be regarded as unique content. Most of today's plagiarism test website banks on the indexed pages in google or other search engine, and they would definitely pass the plagiarism test. But, will google think the same??? or would they in any form store the data offline and identify it.??
I think you should not take a risk if you think it can be dangerous for website ranking. If you want to do experiment then try it by making a blog of some that website whose worth is not as much as this one.
I think it would not be a problem if you do a 301 redirect. In case the blog have expired, but somehow the pages are still in the google index, go to your webmaster tools to remove URL's. And remove the pages from there. In case there are a lot of pages just go ahead and remove the entire folder.
I have done this before. I merge several websites into one and let those other websites to expire and then published those articles to this one website. Didn't notice any problems indexing these pages and they were ranking well in search engines. The site I used was already established PR4 blog so probably it gave me some advantage but still you don't have anything to lose here since content this content is not online elsewhere.
If it only appears one time on the net, it won't be penalized for moving it to a different domain. Read Google's webmaster stuff where it talks about moving a website and do everything you can that they suggest. Sorry about loosing that domain name! wiz
Do not try to do it. The perfect way for you to do it would be getting an access to your old domain and redirecting it to the new one, but it seems you are not able to gain access to it anymore. You may try to place a link to the old site under every article you take from it, so maybe Google will consider it as a quote, but you may get penalized for doing so as well. Pretty risky situation. Are there so much content you want to get back or just a few articles?