Did the distributor tube inside of your water softener break? Before adding more resin to the tank make sure that the distributor tube is not cracked at all. As far as the toilet valves and sinks go you should be able to clear the resin out of the floats. It can be tricky but if you turn off the angle stop which supplys water to your toilet then remove the top of the fill valve. Once the top of the valve is off you can slowly turn the angle stop back on to flush the resin. Keep a hand over this because it may spray. Finally yes it is possible to prevent this from happening in the future. You can install a sediment filter after the water softener so that it will clog if this was to ever happen again. Please let me know if you have any other questions regarding this.