If your asters are like mine (natives) they will come back. They should be poking their little heads out of the earth sometime this month (mine are in a hot and sunny spot and already up and running -- but it would not be unusual for an aster to be dormat, in a less sunny and hot spot), then growing all sumer, and blooming in the fall.

Your Spirea is injured. You should feed it fish emlusion, as often as the packaging on the emulsion allows, and mulch it, and drip water it (put your hose next to it and allow it to drip, drip, drip) overnight whenever it fails to rain for a week or so. Spirea should not really be cut back. If it was just too large for your garden, the better idea is to cut a branches back, let the Spirea recover, and then repeat as necessary. In growing season you might get three gentle trims accomplished, in this fashion.