Will bitcoind save all wallet transactions in prune mode? I have bitcoind running in prune mode (last 10000MiB). Will daemon have info about all my wallet’s transactions or just those that will fit 10000MiB tail?
As long as the wallet is in place before bitcoin core has a chance to
  prune anything, it will work properly
  Reference Link


Let me explain. Basically here is a simplified version of how bitcoind stores wallet transactions:


wallet.dat contains Private Keys | Synced upto Block | Wallet transactions
When new block arrives, bitcoind looks for wallet transactions in the block and adds the ones found into  wallet.dat and also updates Synced upto Block field
In prune mode, older block data is removed, nothing happens to wallet.dat


So if you activate prune mode on a running node, or boot up an old bitcoin node everything should work.
However, if you import an older wallet.dat into already running pruned node, it has to rescan everything from Synced upto Block to find the transactions. This may not be possible due to missing block data