My website has been penalised recently and I have appealed to get it back on Google (as well as changing anything that I think might be related to it).
If that fails and they don’t re-index me, is it possible to do the following:
Move posts / content to new domain.
Add 301 redirect from old domain / posts.
Verify that its the same site but moved via webmaster tools.
Will that help in getting a good rank again in keywords or will they just de-index me again?
Are you sure you site got penalized? If it did just changing domains and redirected is not going to remove the penalty. Remove whatever infraction you did and file the reinclusion request. If you did something bad then you have to pay the penalty and wait.
Moving the old post to new domain is not the solution (Its my thinking only). Because it can also create the copy right and plagiarism issue. Its better to upload new and fresh content on new domain. try to find out duration of penalty and if it is short term then its better to wait for that specific amount of time.