Unless you're talking repairs, there's nothing that the event can do to impede game advancement. And there's definitely some levels of the event that anyone can do without losing a single tank. He can definitely get enough for a Soviet tank pack, maybe even two.
Well, it's a 40% chance at a 5* Soviet tank from the box...and if you pass that hurdle then it's random which particular 5* you get...so it's not all that likely you'll pull her from the box. Probably a better bet to spend the 2K cores and be sure you get her. But I'd take any chances with the boxes for which you might earn enough ornaments/canes before you commit the cores.