I've noticed a couple newer updates on SW's page here:
https://www.southwest.com/html/air/737-MAX-8.html?clk=737MAX8_190408
I bolded a couple pertinent statements in the paragraphs below from that link:
All Boeing MAX 8 aircraft have been removed from our schedule through June 7, 2019.
Our adjusted schedule is already in effect on Southwest.com. Customers who have been impacted by this amended schedule are being proactively notified to adjust their travel plans. We apologize for any inconvenience this may cause.
Also this from the FAQ:
Our goal is to operate our planned schedule with as few cancellations and as minimal an impact to our Customers as possible. To support our Customers, our Teams have worked diligently to increase reliability and reduce the amount of last-minute flight changes caused by the MAX 8 grounding.
Currently, we have amended our flight schedule through June 7, 2019, to incorporate flight changes that will occur as a result of our 34 MAX 8 aircraft being taken out of service. We are taking steps to proactively notify Customers affected by these changes.
Please know that there are still other factors to consider when traveling that have potential to impact a scheduled flight on any given day. These factors include but are not limited to, weather, unscheduled maintenance, operational delays, etc. As your flight date approaches, you can track the status of your flight using our Flight Status Tool on Southwest.com.