There is no way to reignite interest by text, so if there’s a lack of interest, I wouldn’t send any text at all. Good text game is about preserving the magic you created on that approach or on that date. You can’t make new magic. You can blow it, but you can’t repair it. That’s just the nature of the medium.
Regarding your second question, sounds like you might be asking a different question. Are you asking what do you do if she’s not aware that the drink you shared was a date? That’s bad news. If that’s where it stands, you failed you primary objective as a budding Casanova. You failed to express sexual interest.
All of game is about expressing sexual interest while withholding emotional and intellectual interest (until she earns it). If you don’t express that sexual interest, she will see you as a coward, and if you give her too much emotional and intellectual interest, she will see you as needy.
So if you’re walking away from that date, and she doesn’t know it was a date – that you are, at least, sexually interested – you’re going to lose.