By the end of next year, NASCAR will have said goodbye to arguably two of its three biggest stars in a span of two seasons.

This generation’s star power drain has begun. It started with Jeff Gordon, who is wrapping up his final season. Now, with Tony Stewart expected to announce his retirement from stock car racing Wednesday — effective after 2016 — it’s realistic to think more will follow him out the door.

No one can race forever, but many fans hoped Mark Martin’s example — racing and being competitive until his early 50s — would be the model their favorite drivers followed for years to come.

As it turns out, Martin was probably the exception. Gordon is out at 44 years old, and Stewart will be 45 when he retires.

Other top names aren’t getting any younger. Dale Earnhardt Jr. turns 41 next month, so it’s possible NASCAR’s most popular driver for 12 consecutive years and counting will only stick around for another presidential term.

The same goes for six-time champion Jimmie Johnson (40), Kevin Harvick (turns 40 in December) and Matt Kenseth (43).

In all, six of the top nine active drivers on the all-time wins list could be gone by 2020.

So who will replace them?

The first reaction to that question is to look at the young talent coming up through the ranks and throw out names like Chase Elliott, Kyle Larson and Chris Buescher. NASCAR has made a huge push with its “NASCAR Next” talent development program, but those drivers – just like the aforementioned ones – haven’t proven anything yet.

In reality, most of the wins and championships will go to drivers who are already established.

The new NASCAR — let’s say seven years from now — will feature battles between drivers like Brad Keselowski, Joey Logano and Kyle Busch, all of whom will likely have won a championship in that span.

Carl Edwards, Denny Hamlin, Clint Bowyer and Kurt Busch will be the veterans winding down their careers. And they’ll have racked up plenty of wins in the meantime.

But here’s the problem: None of those drivers currently enjoy the fan following of a Stewart, Gordon or Earnhardt. Plus, it doesn’t seem like many drivers coming up through the ranks have the charisma or personality to fill those shoes.

The spotlight will increase on the remaining drivers, to be sure, with NASCAR’s powerful marketing efforts behind them. But will fans be as interested and loyal to the sport without drivers they spent 15 or 20 years following?

This is a familiar question for NASCAR, which has faced such turnover before. The late 1980s and early 90s saw Richard Petty, Bobby Allison and Cale Yarborough hang up their helmets. After Dale Earnhardt’s death in 2001, it was only a handful of years before the generation of drivers that included Bill Elliott, Rusty Wallace and Dale Jarrett stepped away from full-time racing.

NASCAR survived all that turnover. But did it thrive? TV ratings and attendance peaked in the mid-2000s, suffered a steep decline and have continued to gradually slip since. While that downward trend occurred for a number of factors, it’s worth including the absence of some fan favorites as a reason for less interest.

After all, NASCAR is a weekly soap opera on wheels with personalities on full display, and any fan can recite various elements of a driver’s character just as well as the statistics.

In that sense, losing Stewart is a huge blow. He might have been grumpy and prickly at times, but he sure made things interesting, especially when he was running well and mixing it up with other drivers on a weekly basis.

That “Smoke” swagger, mischievous nature and once-in-a-generation pure talent was something to behold. And although it seems to be fading now, fans would prefer to see him in the seat than out of it.

Unfortunately, time eventually wins all the battles — even with legends.

NASCAR can only hope there are more stars waiting for their opportunity to shine.