How do i disable iMessage for a single contact who no longer has an iPhone?

Question

I have a contact who has switched from an iPhone to a Galaxy and my default messaging is iMessage.  In order to get a message to send to her, I have to send the message, then manually resend it as a text message.  Is there a good way to permanently change this so that the default for this contact is no longer iMessage?

Answer 1

I'm looking for a solution on my end that does not require action by the other person.  The person has deregistered from imessage pursuant to Apple's suggestions (http://support.apple.com/en-us/TS5185).  However, the problem remains.  I've deleted the contact from my phone and reentered as not an iphone, and I still cannot text them.  Apple's policy/practice is hindering the use of another company's product. 
Here's where I have a problem with it: (1) The average user doesn't know he has to actively opt out of a service that he didn't actively opt into; (2) it strikes me as a policy that discourages a consumer's free choice (to stop using apple products) by imposing undue and overly burdensome steps to using the full services of another--totally unrelated--company unfettered by some obscure lingering roadblock imposed through a previous business relationship; (3) although Apple offers a service (which did not work in our case), the average user is probably unaware, and therefore, the person who switched services does not necessarily realize that others cannot contact them despite their efforts; and (4) I assume and hope that the 'great minds' at Apple can figure out how to automatically opt non-users out of the imessage service just as it automatically opts in users. 
I did not mean insane in the literal sense, more the colloquial.  However, I did mean unconscionable.  Without going into extensive detail of any number of reasonable hypothetical situations, what if there was an emergency and the person who purchased new services from another company is unable to receive an emergency message?  Say they were unable to receive a phone call because they are in and out of service coverage areas and the only chance of reaching them with an emergency message is via text that will go through when they briefly enter a coverage area?  That, in my opinion, is an example of how this is an unconscionable business practice.