Possible Clues:

• Modern farewell letters
• 'Gotta run,' in a text
• 'Gotta go,' in textspeak
• Short 'goodbye'
• Texter's "bye now"
• 'So long,' for short
• 'Bye for now' in a text
• What best-selling 2004 young adult novel was written entirely in the form of instant messages?
• Texter's "ciao"
• 'Bye for now,' in textspeak