By definition,we use Simple Past if we give past events in the order in which they occured. However, when we look back from a certain time in the past to tell what had happened before, we use Past Perfect.So according to this it would be better to use past perfect instead of simple past tense.
So here it goes:
"I had waited a minute or two after having sent you the text, and since you didn't reply back within 5 minutes,I assumed you were not there and went offline."
Meaning: first I sent you the text,then I waited for about 5 mins and then I went offline because you weren't quick to respond.But before I went offline,I had waited for you.
It is possible to use straight "past tense" but "past perfect" is typically used to emphasize that an action in the past occurred before another action in the past.