Thanks for your question. Sorry for the late reply. I’ve just got back from holidays.
I haven’t read the book ‘90 minutes in heaven’ but I did read an extract from the book on the web and a few book reviews. I must admit I am sceptical of these types of claims. Unfortunately there is not much in the Bible to guide us in this area. Anyway, here’s what I think.
There are obviously cases in the Bible of people who have died being raised to life. Both the prophets Elijah and Elisha raised boys back to life [1 Kings 17:17-24 & 2 Kings 4:32-25]. Jesus raises a number of people from the dead including Lazarus who had been dead for 4 days [Luke 7:11-15; Luke 8:49-56 & John 11:1-49]. Of course there is Jesus resurrection as well. So there is a precedent in the Bible for God bringing people back from the dead.
But as for our state between death and the resurrection, believers are in some sense in communion with Christ while they await the resurrection. [Luke 23:43; Phil 1:23] This is only an intermediate state until the resurrection and the coming of the new heaven and earth. [1 Thess 4:13-17, Rev 21:1ff].
It is possible that Don Piper and others have had such experiences. After all, Stephen, Apostle John and Paul did. The difference is because they were apostles, their writings are authoritative scriptures where as Don Piper’s is not. Personal experiences can be very authentic & edifying. But they can also be misleading and demonic [Matt 7:22]. Personal experiences are hard to refute because they are ‘personal’. Therefore we must always test such experiences against the sure revelation that God had given us - the Bible. [1 Thess 5:18]
If the ‘critics’ are correct and Don Piper is describing a heaven that is largely devoid of Christ, then we should be wary of what weight we give to his testimony.
Here are some links that you might like to follow up. The first two are some book reviews and blog discussions. They are generally critical of the book [not the man], though some do argue proactively for it. The last link is an article by Peter Jensen on how we should weigh and understand spiritual experiences.
I hope this is useful.