I think Leverkusen will continue to play very well and play matches with its main squad in order to break this record in the Bundesliga. Every team playing against Leverkusen will have a hard time, but Dortmund must be very unhappy to miss the victory they came so close to because they were the closest team to beat Leverkusen. After the goal they conceded in extra time, Bayer Leverkusen will continue their efforts to maintain the record.
It's clear to see that Alonso and the players have ambition to finish the league with a unbeaten record. The way the played against Dortmund showed their determination, despite the result wouldn't affect their title hope. This will make their upcoming opponents being extra motivated to be the ones to end their unbeaten streak, which means their upcoming matches tougher.
Alonso needs to make decision on rotating players to avoid fatigue and injuries that could negatively affect their Europa League campaign. However, they have every reason to keep winning, because the unbeaten record will be a positive bargain for their career. It showcases their consistency and ability to perform under pressure, and they hope to attract interest from bigger european clubs to offer higher wages. It's not a secret that players as professionals want to earn bigger if they have a chance to move to a european big club, because Leverkusen is certainly not able to give them big wage.