Quick and dirty example of how one may split the block implementation to multiple files

blocks1.php

<?php

function myblock1() {
  $blocks = array();
  
  $blocks['myblock1'] = array(
    'info' => t("Block 1"),
  );
  
  //...
  
  return $blocks;
}

function myblock1_render() {
  return array('subject' => "Block 1",
    'content' => t("Should be a render array"));
}

blocks2.php

<?php

function myblock2() {
  $blocks = array();
  
  $blocks['myblock2'] = array(
    'info' => t("Block 2"),
  );
  
  //...
  
  return $blocks;
}

function myblock2_render() {
  return array('subject' => "Block 2",
    'content' => t("Should be a render array"));
}

mymodule.module

<?php

function mymodule_block_info() {
  $blocks = array();
  
  //include the files that have block functions.
  module_load_include("php", "mymodule","blocks1");
  module_load_include("php", "mymodule","blocks2");

  //first section of blocks
  $blocks = myblock1();
  $blocks = array_merge($blocks, myblock2());
  //$blocks = array_merge($blocks, myblock3());
  //...
  
  return $blocks;
}

function mymodule_block_view($delta = '') {
  $block = array();
  
  //include the files that have block functions.
  module_load_include("php", "mymodule","includes/blocks1");
  module_load_include("php", "mymodule","includes/blocks2");
  
  //this would require all render functions to contain myblock and end with _render
  if(strstr($delta, "myblock")) {
    $block = call_user_func($delta . "_render");
  }
  
  return $block;
}