Only Hamilton is definitely gone -- he will sign with an agent -- but a source close to the Texas basketball team said that Thompson is "pretty far in and likely to stay in the draft."
"My family and I really took our time with this decision and waited to get a good feel of what this year's draft class would look like and where I can be drafted. With all the information we received, it is best for me to move forward now and pursue this opportunity," Hamilton said.
Joseph is testing the waters in the traditional sense. Thompson, ranked No. 13 overall in ESPN.com draft analyst Chad Ford's prospect rankings, and Joseph have until May 8 to withdraw their names.
"I will continue to gather all the information about my draft status and use that information over the next two weeks to determine whether or not to keep my name in the draft," Thompson said.
For Hamilton, ranked No. 17 in Ford's Top 100 draft prospects, and Thompson, the announcements signal a complete turnaround from what they vowed only a month ago. During the Longhorns' NCAA tournament run, Thompson told reporters, including ESPN.com's Pat Forde, "I'm coming back another year. I've already signed up for summer classes."
Hamilton told multiple media outlets, including the Austin American Statesman that he, too, would be returning.
Those sorts of proclamations, made in the heat of the moment during the NCAA tournament, often raise a skeptical eye. Michael Beasley, Derrick Rose and Greg Oden all once insisted they'd return following their freshmen seasons, too.
But the consensus around Texas is that both Hamilton and Thompson sincerely meant what they said when they said it. Circumstances, however, have changed their opinions.
This NBA draft is more like a game of dominoes, with the decisions of a handful directly knocking into the choices of others. It's easy to chastise Hamilton and Thompson for backtracking on their March Madness promises, but it's also easy to understand what their thinking is.
With North Carolina's Harrison Barnes, Baylor's Perry Jones and Ohio State's Jared Sullinger opting to remain in college, there is more wiggle room at the top half of the draft for everyone. And for someone like Thompson, there is even more space.
Perhaps a late first-round pick if those other players had entered the draft, Thompson now becomes one of the most attractive forwards in what is widely considered a weak draft. He's almost guaranteed to make a significant jump up the draft board and therefore, up the pay scale.
There is no denying the trio's decisions will seriously affect Texas next season. The Longhorns, who looked like a top five team only 24 hours ago, now lose their top two scorers and rebounders in Hamilton and Thompson and, mixed in with the graduation of Gary Johnson, potentially four of their top five scorers.
Rick Barnes will have players to choose from -- incoming freshman and power forward Jonathan Holmes is among the best at his position in his class -- but a team that once seemed to have a lot of answers now instead is left with plenty of questions.
Dana O'Neil covers college basketball for ESPN.com. Information from The Associated Press was used in this report.