Aphid reproduction is complex and not all aphids produce eggs. When they do, egg laying is focused on plants, not the soil. I wouldn't think twice about replanting the container without concern for the soil.

As long as you're not planting brassicas it'll be fine. Going forward if you decide to plant more kale it helps to inspect early and often to keep ahead of the cabbage aphids.

Call me over-cautious, but I'd spray neem oil (harmless to us) on the soil just to be sure. A wee bit goes a long way. But since aphids are decidedly uninterested in soils, it's not really necessary.

However, it would also help to take care of anything else that set up light housekeeping that you didn't notice. Philosophically, I always figure stuff invites friends. :-)