I have not used Google Tasks, but this is how I handle the issue in Outlook.
I attach my first outgoing e-mail message to an Outlook task with a note to myself of the big-picture driver due date, set a reasonable review-again date in the @Waiting For folder, and wait. When the time's up, I forward my original message to the original recipient with a "Do you have any information for me on the attached?" note. That way, he sees the date/time-stamped version of my original request. Repeat as necessary. (My record was 9 layers of messages. In that particular case, I just gave up, as it was clear that he was not going to respond.)
So, I have *zero* undated items in my @NA list or @Waiting For list. Everything has an assigned due date, so that it "bubbles up" to the top of the lists as time marches on. So long as I keep an eye on near-term items, nothing (including follow-up contacts) gets missed.
I hope this helps.