Okay i'll try and make this easy. Souls are like character slots, sparks are about using one of those character slots. When you get in game you'll most likely have a family. Think of your sparks as what retains the skill ramp. When you "perma die" aka when your spark runs out, some of the skills you had will be learned quicker in your next time. You don't keep the skill level, but you level quicker in those skills. So with or without an heir you wouldn't keep your skill level. You could help train your heir in skills you want it to have. Think of heirs as shells that you will move your spark into.

Heirs also make it easier to transfer wealth and items to. As well as owned land businesses homes ect.

In addition if you hold a title of nobility without an official recognized heir (think the almighty contract) the title is more or less up for grabs.

So while you don't have to start over it is infinitely easier to have a set heir.

Aight, Thanks guys! Your both a great help :)

Also unless they changed it, lets say you die and DON'T use the skills you leveled in the past just played life. Then you die again. The first set of skills will still level faster but not as fast because you didn't use them the last life played. Each life you fail to use the previous skills they will level slower. The more lives between using them, less the bonus.