It will probably re-grow, but there are two problems: 1) Even if it wouldn't have gotten whacked, it would have taken many years to begin producing apples, and 2) Apple trees grown from seed don't produce the same type of apple, so you could grow this for the next 5-10 years and then find out that the apples were inedible. If it's just a fun experiment to grow from seed, that's fine. But if you actually want a tree producing edible apples any time soon, spend 30 bucks on a tree at a big box store or a nursery.

Thanks for the reply. You are correct saying it was more of a horticultural experiment, I wasn't really interested in fruit (which can be problematic under the best circumstances), just wanted a small tree to embellish the front yard. It was just a sentimental plant.

A week since the incident. It looks like it has a small shoot of new growth.

Congratulations on the new shoot! If you have mulch around the seedling at least a foot from any edge to the seedling it's less likely to get weed wacked. The mower is going to wack around those bricks and the string may be long enough to also get the seedling.

If you have rabbits around you will want to cage it to protect it from them as well.

tj