The crisis at Twitter reached a new peak on Thursday night as hundreds of employees were reported to have rejected Elon Musk’s ultimatum to keep working for the business, threatening its ability to keep operating.

As the company temporarily closed its offices to staff, Twitter users began saying their goodbyes and linking to accounts on other platforms.

#RIPTwitter, #TwitterDown, Mastodon and Myspace were all trending on the platform after the deadline passed on Musk’s ultimatum for the remaining workforce to sign up for “long hours at high

The departures include many engineers responsible for fixing bugs and preventing service outages, raising questions about the stability of the platform amid the loss of employees and prompting hurried debates among managers over who should be asked to return, current and former employees said.

In an early sign that the number of those declining to sign was greater than anticipated, Musk eased off a return-to-office mandate he had issued a week ago, telling employees on Thursday they would be allowed to work remotely if their managers asserted they were making “an excellent contribution”.

Twitter later announced via email that it would close “our office buildings” and disable employee badge access until Monday, the New York Times reported.

Online, users were speculating that the site could go down in a matter of hours or days.

On Thursday evening, the version of the Twitter app used by employees began slowing down, according to one source familiar with the matter, who estimated that the public version of Twitter was at risk of breaking during the night. Website DownDetector reported a significant uptick in user reports of issues on the site.

 “If it does break, there is no one left to fix things in many areas,” the person said, who declined to be named for fear of retribution.

The news prompted an outpouring of grief on the platform, and prompted many users to link to their accounts on Instagram or Mastodon as an alternative.

US representative Alexandria Ocasio-Cortez tweeted she could be found on Instagram or on email.

She followed up with a tweet saying those employees who built the company deserved better. “Shout out to all the workers at Twitter. You all built a vital place for connection and deserved so much better,” she said.

Official government accounts also began providing means of being found elsewhere.

Musk was meeting some top employees to try to convince them to stay, said one current employee and a recently departed employee who was in touch with Twitter colleagues.

In a private chat on Signal with about 50 Twitter staffers, nearly 40 said they had decided to leave, according to the former employee.

And in a private Slack group for Twitter’s current and former employees, about 360 people joined a new channel titled “voluntary-layoff”, said a person with knowledge of the Slack group.

A separate poll on Blind asked staffers to estimate what percentage of people would leave Twitter based on their perception. More than half of respondents estimated at least 50% of employees would leave.

While it is unclear how many employees have chosen to stay, the numbers highlight the reluctance of some staffers to remain at a company where Musk has hastened to fire half its employees including top management, and is ruthlessly changing the culture to emphasise long hours and an intense pace.

Twitter, which has lost many of its communication team members, did not respond to a request for comment.

Blue hearts and salute emojis flooded the site and its internal chatrooms on Thursday, the second time in two weeks as Twitter employees said their goodbyes.

By 6pm EST, more than two dozen Twitter employees across the United States and Europe had announced their departures in public Twitter posts reviewed by Reuters, though each resignation could not be independently verified.

Early on Wednesday, Musk had emailed Twitter employees, saying: “Going forward, to build a breakthrough Twitter 2.0 and succeed in an increasingly competitive world, we will need to be extremely hardcore.”

The email asked staff to click “yes” if they wanted to stick around. Those who did not respond by 5pm eastern time on Thursday would be considered to have quit and given a severance package, the email said.

As the deadline approached, employees scrambled to figure out what to do.

One team within Twitter decided to take the leap together and leave the company, one employee who is leaving told Reuters.

In an apparent jab at Musk’s call for employees to be “hardcore”, the Twitter profile bios of several departing engineers on Thursday described themselves as “softcore engineers” or “ex-hardcore engineers”.