Also I just found out that on the person's iPhone I'm borrowing, there's a setting in Settings > Messages > Send as SMS (Send as SMS when iMessage is unavaible. Carrier messaging rates may apply), and it's OFF by default, which makes very little sense. The message I had sent in my post above never timed out and went through as green, so I turned the setting for Send as SMS on and tried texting again. Started out as a blue iMessage, timed out after a few minutes, and sent as a green SMS and went through. The placeholder text in the input box changed from iMessage to Text Message. So I figured good to go from here on, at least for this person's iPhone at least. I deleted the text thread, and tried to retext myself, started out as iMessage again.. so no good.
Here's the important part
Just hung up with Apple, here's what I was told:
The tech told me this is a flaw with iOS that was supposed to have been addressed in iOS 7.1. He thought I had found a solution by setting "Send as SMS" in Settings > Messages to On. He told me until a fix for this comes out, I should tell all the people who have iPhones who have my phone number to go to their settings and turn it on (not even going to comment on how I feel about this). Obviously this isn't even a working solution. He then said that it's an issue with the iPhone's caching, that it's still associating my phone number to an iPhone, and that the token in the cache will expire in 45 days, and that's when it should renew the token and disassociate the phone number as an iPhone user and permanently switch to regular SMS.
So here's the bottom line: for at least 45 days, and possibly, maybe even not, if an iPhone user tries to send you a text, and they don't notice that the blue message never got a "Delivered" subtext, they'll think you're ignoring them, unless they know (because you've contacted all your iPhone users in your contacts) to go into their settings to turn on the aformentioned setting. If they text you and get an "Unable to Deliver" message with a red exclamation mark, they'll think you've disconnected your phone number, because just like the person I found out from today that this is what happened to them when they tried to text me, there's a very good chance that they won't be able to figure out that you can click on the red exclamation or hold down on the message to get a menu and hit "Send as Text Message". Soooo we'll see in 45 days then. I'm pretty sure this isn't a priority for Apple to fix since it's for people who no longer use their products.