Under the new Marriott program all lifetime elites kept their current lifetime status from either program and everyone had until December 31 to earn lifetime status under old program rules despite the new program requiring more elite nights than Starwood had insisted upon and no longer required minimum points for status as Marriott had.
One quirk of the new program though is that it will not offer lifetime status higher than Platinum (50 nights). Legacy Marriott lifetime Platinums were 75 night platinums so got to keep lifetime 75 night elite. Starwood members with similar lifetime activity nearly lost their cookies over this.