You can certainly restart a sour that has separated. Just feed it as you normally would. It may take a few feedings to get active again. You can store sourdough in the fridge for extended periods of time. Use the white stuff not the clear liquid to restart your sour.
Not trying to rain on the parade. Just debunking a myth. I hear this all the time and people "knead" to know what is really going on. I have no doubt these starters are a point of pride for families. I didn't tell anyone to stop feeding them or not use them. Just don't think it is the same as...
Over time, sourdough starters change to reflect the bacteria present where they live. That's why it is crap to buy a "Klondike" or "San Fransisco" starter. That said. There is nothing wrong with experimenting. Just don't think it is the same as in 1904. Very romantic, just not true.