While I’m happy for Nico Rosberg as he gets to on a high note after a Formula One world drivers’ championship, I have to wonder what this means for excitement in the sport next year. Rosberg’s retirement ends the heated rivalry that’s defined the past few years of F1 and thus, signifies the end of an era.

For race after race in 2015 and 2016, Rosberg and Lewis Hamilton—Mercedes teammates, longtime associates and often bitter rivals on and off the track—battled for points and titles and legacy.

Perhaps this hasn’t been the most enjoyable era of F1, as only Mercedes seemed to nail the V6 hybrid turbo formula right out of the gate. Pretty much every other team has been left in catch-up mode ever since, giving Mercedes three constructors’ championships in a row that came far too easily.

While it must be said that they were in the right car at the right time, the constant battle between the ultra-talented driver duo of Hamilton and Rosberg was no small part of Mercedes’ championship three-peat.

And oh, did they ever get under each others’ skin.

Here were two racers who’d known each other since childhood, and by the time they ended up on the same F1 team, there was no greater burning desire than their insatiable need to beat their teammate.

The rivalry didn’t just play out on track, but in comments and mind games outside the racing as well. Every word that came out of Hamilton’s or Rosberg’s mouths about their teammate was pure dramatic gold. For years, many even assumed that Hamilton had the upper hand, as he tended to be the more outspoken and outwardly confident of the two, and that Rosberg had fallen in line as a number two driver. Rosberg admitted in his retirement statements this morning that losing to an often cocky Hamilton only made him need—this was no want, but a basic, primal need—to win more.

Rosberg specifically mentioned the 2015 United States Grand Prix where Hamilton at the first corner in his press conference today, where Rosberg announced his retirement to the masses. That move and the that followed was the ultimate boiling-over of the Hamilton vs. Rosberg rivalry. Hamilton had just clinched his , and Hamilton’s swagger was just too much for Rosberg to bear after that first-corner move.

2015 World Drivers’ Champion Lewis Hamilton was especially ruthless to teammate Nico Rosberg during

Because the Mercedes cars were so dominant, though, if we wanted front-of-grid drama and action, Rosberg vs. Hamilton was often the only battle we had. The performance of F1 cars has been so lopsided that it was no longer a question of “who will win?” for most races. It was, “which Mercedes is going to win?”

Even when it was the same team winning every week, it made for good racing, the kind we’ll look back on as one that defined this era.

And Rosberg’s now-final race, last weekend’s Abu Dhabi Grand Prix, was so notable for a battle with Hamilton. Hamilton ultimately won the race, but his clever tactic of cruising around slowly at the end made Rosberg vulnerable to getting knocked off the podium and not scoring enough points. Rosberg, however, did what he whatever possible to take and keep second place and ultimately scored enough points to claim the championship.

With only Hamilton left at Mercedes and much of the rest of the grid seemingly locked down for 2017, it raises so many questions. Already, we have a for the cars coming in 2017, which is a major redesign.

Most fans are hoping that more teams are competitive, but what if they’re not? And what if Mercedes opts to avoid the drama of having two competitive drivers and signs someone markedly less talented than Hamilton to fill Rosberg’s seat?

Should Mercedes emerge in 2017 with another dominant car—which is a possibility, given how well resourced and connected they are in the sport—replacing Rosberg with a true number two driver would be the worst possible situation. Hamilton would cruise home to too many uninteresting, unchallenged wins. That’s not racing. That’s leading a parade.

Mercedes has the tough—and probably expensive, knowing that contracts might need breaking this late in the game—job of finding someone who can bring the heat to Hamilton like Rosberg did. For the sake of the sport and its ability to keep us all entertained, I hope they can pull it off.