No point. If it's truely been de-indexed, it's for good reason... and no, it's not buying backlinks. Sites get de-indexed for being part of blog networks as in you're selling links on the site, being hacked (whether you are aware of it or not), email spam coming from site, mass copyright infringement, anything illegal, etc.
If you're not guilty of any of these things, contact google and see if they will answer (they might). Disavowing/reconsideration requests, will do nothing but waste your time.