Robert Mueller has finished his report and turned it over to the AG. Multiple people were indicted over the course of this investigation. Now that it has concluded, is it a safe assumption that all indictments have been handed down? Or is there a way more could be announced in the future, as they are laid out in the report?
New indictments in the Mueller report
Mr. Mueller did not suggest additional charges as part of his investigation, when he delivered his findings to Mr. Barr on Friday. This caps the special counsel’s charges at 199, filed against 34 people and three companies.
The “principal conclusions” of the special counsel investigation, which Mr. Barr said he might be able to share with lawmakers in the coming days, are not likely to include many details. In a letter to lawmakers, Mr. Barr said he would consult with Mr. Mueller and the deputy attorney general, Rod J. Rosenstein, about what other information from the report can be released.
In answer to your questions:
Now that it has concluded, is it a safe assumption that all indictments have been handed down? Or is there a way more could be announced in the future, as they are laid out in the report?
If the reporting by the NYT is correct, there will be no further indictments as part of the Mueller Investigation. That doesn't mean there may not be any other indictments from investigations that were started based on the Mueller Investigation but taken over by other offices.
An example of such a 'spin-off' investigation started with a search warrant for Michael Cohen's emails (then Trump's lawyer)(July 2017) by the Mueller probe then a raid on his office (April 2018) by the SDNY. In december 2018 this led to Cohen being sentenced by the SDNY, according to the Guardian:
Michael Cohen, Donald Trump’s longtime personal fixer, was sentenced to 36 months in prison in New York on Wednesday for crimes including lying to Congress and facilitating illegal payments to silence two women who alleged affairs with Trump.
According to the New York Times there are still about a dozen (12) of such investigations going on:
Even as the special counsel, Robert S. Mueller III, submitted his confidential report to the Justice Department on Friday, federal and state prosecutors are pursuing about a dozen other investigations that largely grew out of his work, all but ensuring that a legal threat will continue to loom over the Trump presidency.